xfs: use xfs_defer_finish_one to finish recovered work items

Get rid of the open-coded calls to xfs_defer_finish_one.  This also
means that the recovery transaction takes care of cleaning up the dfp,
and we have solved (I hope) all the ownership issues in recovery.

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