Rename the mmap_sem field to mmap_lock. Any new uses of this lock
should now go through the new mmap locking api. The mmap_lock is
still implemented as a rwsem, though this could change in the future.
Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>