lib: reuse page_ext_data() to obtain codetag_ref

codetag_ref_from_page_ext() reimplements the same calculation as
page_ext_data().  Reuse existing function instead.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: dcfe378 ("lib: introduce support for page allocation tagging")
Signed-off-by: Suren Baghdasaryan <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: Pasha Tatashin <[email protected]>
Cc: Sourav Panda <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: surenbaghdasaryan

include/linux/pgalloc_tag.h

@@ -15,7 +15,7 @@ extern struct page_ext_operations page_alloc_tagging_ops;
 
 static inline union codetag_ref *codetag_ref_from_page_ext(struct page_ext *page_ext)
 {
-	return (void *)page_ext + page_alloc_tagging_ops.offset;
+	return (union codetag_ref *)page_ext_data(page_ext, &page_alloc_tagging_ops);
 }
 
 static inline struct page_ext *page_ext_from_codetag_ref(union codetag_ref *ref)