mm/page_ext: use page_ext_data helper in page_table_check

Use page_ext_data helper in page_table_check to avoid access offset
directly.

Link: https://lkml.kernel.org/r/20230718145812.1991717-3-shikemeng@huaweicloud.comSigned-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Andrew Morton <akpm@linux-foudation.org>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_table_check.c

@@ -51,7 +51,7 @@ struct page_ext_operations page_table_check_ops = {
 static struct page_table_check *get_page_table_check(struct page_ext *page_ext)
 {
 	BUG_ON(!page_ext);
-	return (void *)(page_ext) + page_table_check_ops.offset;
+	return page_ext_data(page_ext, &page_table_check_ops);
 }
 
 /*