dm bio prison: use rb_entry() rather than container_of()

To make the code clearer, use rb_entry() instead of container_of() to
deal with rbtree.

Signed-off-by: Geliang Tang <[e-mail]>
Acked-by: Coly Li <[e-mail]>
Signed-off-by: Mike Snitzer <[e-mail]>

drivers/md/dm-bio-prison-v1.c

···
 
 	while (*new) {
 		struct dm_bio_prison_cell *cell =
-			container_of(*new, struct dm_bio_prison_cell, node);
+			rb_entry(*new, struct dm_bio_prison_cell, node);
 
 		r = cmp_keys(key, &cell->key);
 

drivers/md/dm-bio-prison-v2.c

···
 
 	while (*new) {
 		struct dm_bio_prison_cell_v2 *cell =
-			container_of(*new, struct dm_bio_prison_cell_v2, node);
+			rb_entry(*new, struct dm_bio_prison_cell_v2, node);
 
 		r = cmp_keys(key, &cell->key);