block: don't pass BIOSET_NEED_BVECS for q->bio_split

q->bio_split is only used by bio_split() for fast cloning bio, and no
need to allocate bvecs, so remove this flag.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Tested-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -531,7 +531,7 @@ struct request_queue *blk_alloc_queue(int node_id)
 	if (q->id < 0)
 		goto fail_q;
 
-	ret = bioset_init(&q->bio_split, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
+	ret = bioset_init(&q->bio_split, BIO_POOL_SIZE, 0, 0);
 	if (ret)
 		goto fail_id;