xfs: quota scrub should use bmapbtd scrubber

Replace the quota scrubber's open-coded data fork scrubber with a
redirected call to the bmapbtd scrubber.  This strengthens the quota
scrub to include all the cross-referencing that it does.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>