btrfs: use common helper instead of open coding a bit test

The helper does the same math and we take care about the special case
when flags is 0 too.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2018-09-21 14:26:34 +02:00
commit 818255feec