xfs_scrub: fix estimate of work items for phase 4

Codex complains that the number of work items computed when estimating
the amount of work for phase 4 doesn't include the FSCOUNTERS and
QUOTACHECK items.  Add them back in.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>