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.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>