mmap locking API: fix missed mmap_sem references in comments

Commit c1e8d7c6 ("mmap locking API: convert mmap_sem comments") missed
replacing some references of mmap_sem by mmap_lock due to misspelling
(mm_sem instead of mmap_sem).

Link: https://lkml.kernel.org/r/20220503113333.214124-1-mail@florommel.de


Signed-off-by: Florian Rommel <mail@florommel.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>