btrfs: account as waiting for IO, while waiting fot the flush bio completion

Similar to what submit_bio_wait does, we should account for IO while
waiting for a bio completion. This has marginal visible effects, flush
bio is short-lived.

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2017-06-15 16:04:26 +02:00
commit 2980d5745f