btrfs: Pass 0 for bio_offset to btrfs_wq_submit_bio

Buffered writeback always calls btrfs_csum_one_bio with the last 2
arguments being 0 irrespective of what the bio_offset has been passed to
btrfs_submit_bio_start. Make this apparent by explicitly passing 0 for
bio_offset when calling btrfs_wq_submit_bio from btrfs_submit_bio_hook.
This will allow for further simplifications down the line. No functional
changes.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -1991,8 +1991,7 @@ static blk_status_t btrfs_submit_bio_hook(struct inode *inode, struct bio *bio,
 			goto mapit;
 		/* we're doing a write, do the async checksumming */
 		ret = btrfs_wq_submit_bio(fs_info, bio, mirror_num, bio_flags,
-					  bio_offset, inode,
-					  btrfs_submit_bio_start);
+					  0, inode, btrfs_submit_bio_start);
 		goto out;
 	} else if (!skip_sum) {
 		ret = btrfs_csum_one_bio(inode, bio, 0, 0);