fs: convert to bio_last_bvec_all()

This patch converts 3 users to bio_last_bvec_all(), so that we can go
ahead and convert to multipage bvec.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/fs/buffer.c b/fs/buffer.c
index 0736a6a..8b26295 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3014,7 +3014,7 @@ static void end_bio_bh_io_sync(struct bio *bio)
 void guard_bio_eod(int op, struct bio *bio)
 {
 	sector_t maxsector;
-	struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
+	struct bio_vec *bvec = bio_last_bvec_all(bio);
 	unsigned truncated_bytes;
 	struct hd_struct *part;