mm: correct typo in MMAP_STATE() macro

mm: correct typo in MMAP_STATE() macro

We mistakenly refer to len rather than len_ here.  The only existing
caller passes len to the len_ parameter so this has no impact on the code,
but it is obviously incorrect to do this, so fix it.

Link: https://lkml.kernel.org/r/20241118175414.390827-1-lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Jann Horn <jannh@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>