The status of flush bio is tracked as a status bit, changed in commit 1c3063b6dbfa ("btrfs: cleanup device states define
BTRFS_DEV_STATE_FLUSH_SENT"), the flush_bio_sent was forgotten.
Reviewed-by: Anand Jain <anand.jain@oracle.com> Signed-off-by: David Sterba <dsterba@suse.com>