block: merge: get the 1st and last bvec via helpers

This patch applies the two introduced helpers to
figure out the 1st and last bvec.

Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 888a7fe..2613531 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -304,7 +304,6 @@
 				   struct bio *nxt)
 {
 	struct bio_vec end_bv = { NULL }, nxt_bv;
-	struct bvec_iter iter;
 
 	if (!blk_queue_cluster(q))
 		return 0;
@@ -316,11 +315,8 @@
 	if (!bio_has_data(bio))
 		return 1;
 
-	bio_for_each_segment(end_bv, bio, iter)
-		if (end_bv.bv_len == iter.bi_size)
-			break;
-
-	nxt_bv = bio_iovec(nxt);
+	bio_get_last_bvec(bio, &end_bv);
+	bio_get_first_bvec(nxt, &nxt_bv);
 
 	if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
 		return 0;