dm bio prison v1: prepare to intelligently size dm_bio_prison's prison_regions

Add num_locks member to dm_bio_prison struct and use it rather than
the NR_LOCKS magic value (64).

Next commit will size the dm_bio_prison's prison_regions according to
dm_num_sharded_locks().

Signed-off-by: Mike Snitzer <snitzer@kernel.org>
1 file changed