Fixing wpdb->get_results and wpdb->prepare?

Question

So I have been using the theme Vilan from ThemeForest. Along with the theme come a couple of plugins, of which one is Revolution Slider. I'm also using Bedrock by Roots. I'm getting the following error:

Notice: wpdb::prepare was called incorrectly. The query argument of wpdb::prepare() must have a placeholder. Please see Debugging in WordPress for more information. (This message was added in version 3.9.) in /Applications/MAMP/htdocs/localppl/web/wp/wp-includes/functions.php on line 3547.

It wouldn't bother me except that the WordPress Gallery gets stuck on loading whenever displaying on grid mode. I found out the error is coming from Revolution slider, because I turned it off and on and the problem would appear and disappear whenever I did so. I tried to track back the problem and I found it would work fine once I removed the code below. Now, I'm sure the problem is with the database call, but I don't know how to fix it (I'll use a child theme to replace the filter).

It works fine once I remove the prepare call, but I read that it is used to prevent SQL injections. Even if, I still want to learn how to fix this while using it, if possible.

 if (is_plugin_active('revslider/revslider.php')) {
 global $wpdb;

  $rs_table_name = $wpdb->prefix . "revslider_sliders";
  $rs = $wpdb->get_results( $wpdb->prepare("SELECT id, title, alias FROM $rs_table_name ORDER BY id ASC LIMIT 999", '') );

 $revsliders = array();
 if ($rs) {
     foreach ( $rs as $slider ) {
       $revsliders[$slider->alias] = $slider->alias;
     }
 } else {
     $revsliders["No sliders found"] = 0;
 }

 // Page header slideshow metabox
 $meta_boxes[] = array(
         // Meta box id, UNIQUE per meta box. Optional since 4.1.5
         'id' => 'general_page_header_slideshow_meta',

         // Meta box title - Will appear at the drag and drop handle bar. Required.
         'title' => __( 'Page Header Slideshow', 'okthemes' ),

         // Post types, accept custom post types as well - DEFAULT is array('post'). Optional.
         'pages' => array( 'page' ),

         // Where the meta box appear: normal (default), advanced, side. Optional.
         'context' => 'normal',

         // Order of meta box: high (default), low. Optional.
         'priority' => 'high',

         // Auto save: true, false (default). Optional.
         'autosave' => true,

         // List of meta fields
         'fields' => array(
                 array(
                     'name'  => 'Page header slider',
                     'id'    => "{$prefix}page_header_slider",
                     'desc'  => 'Enable/Disable page header slider.',
                     'std'   => 0,
                     'type'  => 'checkbox',
                 ),

                 // SELECT BOX
                 array(
                     'name'     => __( 'Select the page header slider', 'okthemes' ),
                     'id'       => "{$prefix}page_header_slider_select",
                     'type'     => 'select',
                     // Array of 'value' => 'Label' pairs for select box
                     'options'  => $revsliders,
                     // Select multiple values, optional. Default is false.
                     'multiple'    => false,
                     'std'         => '',
                     'placeholder' => __( 'Select a slider', 'okthemes' ),
                 ),

         ),

 );
 } //end check for rev slider

Answer 1

As per suggestion by Milo, I removed the prepare statement, and it worked beautifully:

$rs = $wpdb->get_results( "SELECT id, title, alias FROM $rs_table_name ORDER BY id ASC LIMIT 999" );

I then came to try and overwrite it through a child theme. It was being added to a filter originally in the parent theme:

add_filter( 'rwmb_meta_boxes', 'gg_register_meta_boxes' );

I struggled as to how I could replace the filter; a simple remove and add of another function didn't solve it, but I had to add the remove_filter to an action hook in order to overwrite the parent theme functions: after_setup_theme.

I solved that through the following code:

// Change Parent Theme Features
add_action( 'after_setup_theme', 'change_parent_theme_features', 10 );

function change_parent_theme_features() {
    remove_filter( 'rwmb_meta_boxes', 'gg_register_meta_boxes' );
}

Finally, I added the amended function to the above filter.