mm/rmap: not necessary to mask off FOLIO_PAGES_MAPPED

mm/rmap: not necessary to mask off FOLIO_PAGES_MAPPED

At this point, we are in an if branch conditional on (nr <
ENTIRELY_MAPPED), and FOLIO_PAGES_MAPPED is equal to (ENTIRELY_MAPPED -
1).  This means the upper bits are already cleared.

It is not necessary to mask it off.

Link: https://lkml.kernel.org/r/20250817032647.29147-2-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Harry Yoo <harry.yoo@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>