xfs: replace no-op firstblock init with ->t_firstblock

xfs_refcount_recover_cow_leftovers() has no need for a firstblock
variable and so passes an unrelated xfs_fsblock_t to
xfs_defer_init() to avoid declaring one. Replace this no-op
initialization with ->t_firstblock. This will be optimized away by
the removal of the xfs_defer_init() firstblock param.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/libxfs/xfs_refcount.c

@@ -1691,7 +1691,7 @@ xfs_refcount_recover_cow_leftovers(
 		trace_xfs_refcount_recover_extent(mp, agno, &rr->rr_rrec);
 
 		/* Free the orphan record */
-		xfs_defer_init(tp, &dfops, &fsb);
+		xfs_defer_init(tp, &dfops, &tp->t_firstblock);
 		agbno = rr->rr_rrec.rc_startblock - XFS_REFC_COW_START;
 		fsb = XFS_AGB_TO_FSB(mp, agno, agbno);
 		error = xfs_refcount_free_cow_extent(mp, tp->t_dfops, fsb,