Sorting Products by SKU

I want to sort products in the admin side by SKU.

add_filter(‘woocommerce_get_catalog_ordering_args’, ‘am_woocommerce_catalog_orderby’);
function am_woocommerce_catalog_orderby( $args ) {
$args[‘orderby’] = ‘meta_value’;
$args[‘meta_key’] = ‘_sku’;
$args[‘order’] = ‘asc’;

}

It doesn’t seem to work.