mm: correct misleading comment on mmap_lock field in mm_struct

mm: correct misleading comment on mmap_lock field in mm_struct

The comment previously described the offset of mmap_lock as 0x120 (hex),
which is misleading.  The correct offset is 56 bytes (decimal) from the
last cache line boundary.  Using '0x120' could confuse readers trying to
understand why the count and owner fields reside in separate cachelines.

This change also removes an unnecessary space for improved formatting.

Link: https://lkml.kernel.org/r/20250806145906.24647-1-adrianhuang0701@gmail.com
Signed-off-by: Adrian Huang (Lenovo) <adrianhuang0701@gmail.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>