You can simply store the basename in a variable in the main file and reference that variable in the admin file.
If you are using classes, which I determine from your example code, you can simply create a static property in you main class and reference that in the admin class:
class My_Plugin {
static $basename = null;
public function __construct {
$this->basename = plugin_basename(__FILE__);
}
}
class My_Plugin_Admin {
public function change_action_links() {
add_filter( 'plugin_action_links_' . My_Plugin::$basename, array( $this, 'add_action_links' ) );
}
}