mm/ksm: replace set_page_stable_node by folio_set_stable_node

mm/ksm: replace set_page_stable_node by folio_set_stable_node

Only single page could be reached where we set stable node after write
protect, so use folio converted func to replace page's.  And remove the
unused func set_page_stable_node().

Link: https://lkml.kernel.org/r/20240411061713.1847574-11-alexs@kernel.org
Signed-off-by: Alex Shi (tencent) <alexs@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>