bcache: convert to bioset_init()/mempool_init()

Convert bcache to embedded bio sets.

Reviewed-by: Coly Li <colyli@suse.de>
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/bcache/bset.h

@@ -347,7 +347,7 @@ static inline struct bkey *bch_bset_search(struct btree_keys *b,
 /* Sorting */
 
 struct bset_sort_state {
-	mempool_t		*pool;
+	mempool_t		pool;
 
 	unsigned		page_order;
 	unsigned		crit_factor;