mm: remove cast from page_to_nid()

Now that PF_POISONED_CHECK() can take a const argument, we can drop
the cast.

Link: https://lkml.kernel.org/r/20240227192337.757313-9-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -1641,13 +1641,11 @@ static inline int page_zone_id(struct page *page)
 }
 
 #ifdef NODE_NOT_IN_PAGE_FLAGS
-extern int page_to_nid(const struct page *page);
+int page_to_nid(const struct page *page);
 #else
 static inline int page_to_nid(const struct page *page)
 {
-	struct page *p = (struct page *)page;
-
-	return (PF_POISONED_CHECK(p)->flags >> NODES_PGSHIFT) & NODES_MASK;
+	return (PF_POISONED_CHECK(page)->flags >> NODES_PGSHIFT) & NODES_MASK;
 }
 #endif