display all products from subcategories OC
$data = array(
'filter_category_id' => $top_category,
'filter_sub_category' => true,
'sort' => $sort,
'order' => $order,
'start' => ($page - 1) * $limit,
'limit' => $limit
);
$product_total = $this->model_catalog_product->getTotalProducts($data);