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>

fs/btrfs/compression.c

@@ -411,7 +411,7 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
 
 static u64 bio_end_offset(struct bio *bio)
 {
-	struct bio_vec *last = &bio->bi_io_vec[bio->bi_vcnt - 1];
+	struct bio_vec *last = bio_last_bvec_all(bio);
 
 	return page_offset(last->bv_page) + last->bv_len + last->bv_offset;
 }

fs/btrfs/extent_io.c

@@ -2724,7 +2724,7 @@ static int __must_check submit_one_bio(struct bio *bio, int mirror_num,
 				       unsigned long bio_flags)
 {
 	blk_status_t ret = 0;
-	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
+	struct bio_vec *bvec = bio_last_bvec_all(bio);
 	struct page *page = bvec->bv_page;
 	struct extent_io_tree *tree = bio->bi_private;
 	u64 start;

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;