xfs_scrub: use repair_item to direct repair activities

xfs_scrub: use repair_item to direct repair activities

Now that the new scrub_item tracks the state of any filesystem object
needing any kind of repair, use it to drive filesystem repairs and
updates to the in-kernel health status when repair finishes.

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