Writing a wordpress plugin, trying to retrieve data from customized table?

I am trying to create a wordpress plugin. I had created a table and trying to retrieve data from the table but it give me an error message

Warning: Missing argument 2 for wpdb::prepare(), called in
/home2/l2on708/public_html/mysite.com/wp-content/plugins/myplugin/myplugin.php
on line 79 and defined in
/home2/l2on708/public_html/mysite.com/wp-includes/wp-db.php on line
1210

<?php
$table_name = $wpdb->prefix . "gallery_rating"; 


function options_page(){
    /*
    *  displaying back-end plugin page 
    */
    global $table_name;
    global $wpdb;


    $stmt = $wpdb->prepare("SELECT * FROM $table_name ORDER BY id DESC LIMIT 1 ");  
    $stmt->execute();
    $rows = $stm->fetchALL(PDO::FETCH_ASSOC);
    foreach ($rows as $rows) {

      $options_link = $rows['link'];
   }

   }


function table_install () {
      global $wpdb;
      global $table_name;


      $charset_collate = $wpdb->get_charset_collate();

      $sql = "CREATE TABLE $table_name (
        id mediumint(9) NOT NULL AUTO_INCREMENT,
        link varchar(100) NOT NULL,
        src varchar(250) NOT NULL,
        click int(11) NOT NULL,
        UNIQUE KEY id (id)
      ) $charset_collate;";

      require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );
      dbDelta( $sql );
   }   
   // run the install scripts upon plugin activation
   register_activation_hook(__FILE__,'table_install');
?>