mm/page_ext: use page_ext_data helper in page_owner

Use page_ext_data helper in page_owner to avoid access offset directly.

Link: https://lkml.kernel.org/r/20230718145812.1991717-4-shikemeng@huaweicloud.com
Signed-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_owner.c

@@ -104,7 +104,7 @@ struct page_ext_operations page_owner_ops = {
 
 static inline struct page_owner *get_page_owner(struct page_ext *page_ext)
 {
-	return (void *)page_ext + page_owner_ops.offset;
+	return page_ext_data(page_ext, &page_owner_ops);
 }
 
 static noinline depot_stack_handle_t save_stack(gfp_t flags)