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: NGeliang Tang <geliangtang@gmail.com>
Acked-by: NColy Li <colyli@suse.de>
Signed-off-by: NMike Snitzer <snitzer@redhat.com>

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

@@ -116,7 +116,7 @@ static int __bio_detain(struct dm_bio_prison *prison,
 
 	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

@@ -120,7 +120,7 @@ static bool __find_or_insert(struct dm_bio_prison_v2 *prison,
 
 	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);