Btrfs: fix compilation errors under DEBUG

bi_sector and bi_size moved to bi_iter since commit 4f024f3797c4
("block: Abstract out bvec iterator")

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/volumes.c

@@ -5709,8 +5709,8 @@ static void submit_stripe_bio(struct btrfs_root *root, struct btrfs_bio *bbio,
 		name = rcu_dereference(dev->name);
 		pr_debug("btrfs_map_bio: rw %d, sector=%llu, dev=%lu "
 			 "(%s id %llu), size=%u\n", rw,
-			 (u64)bio->bi_sector, (u_long)dev->bdev->bd_dev,
-			 name->str, dev->devid, bio->bi_size);
+			 (u64)bio->bi_iter.bi_sector, (u_long)dev->bdev->bd_dev,
+			 name->str, dev->devid, bio->bi_iter.bi_size);
 		rcu_read_unlock();
 	}
 #endif