xfs: simplify usage of the rcur local variable in xfs_refcount_finish_one

Only update rcur when we know the final *pcur value.
Inspired-by: Christoph Hellwig <hch@lst.de>
[djwong: don't leave the caller with a dangling ref]
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_refcount.c

@@ -1341,7 +1341,7 @@ xfs_refcount_finish_one(
 	struct xfs_btree_cur		**pcur)
 {
 	struct xfs_mount		*mp = tp->t_mountp;
-	struct xfs_btree_cur		*rcur;
+	struct xfs_btree_cur		*rcur = *pcur;
 	struct xfs_buf			*agbp = NULL;
 	int				error = 0;
 	xfs_agblock_t			bno;
@@ -1359,7 +1359,6 @@ xfs_refcount_finish_one(
 	 * If we haven't gotten a cursor or the cursor AG doesn't match
 	 * the startblock, get one now.
 	 */
-	rcur = *pcur;
 	if (rcur != NULL && rcur->bc_ag.pag != ri->ri_pag) {
 		nr_ops = rcur->bc_refc.nr_ops;
 		shape_changes = rcur->bc_refc.shape_changes;
@@ -1373,11 +1372,11 @@ xfs_refcount_finish_one(
 		if (error)
 			return error;
 
-		rcur = xfs_refcountbt_init_cursor(mp, tp, agbp, ri->ri_pag);
+		*pcur = rcur = xfs_refcountbt_init_cursor(mp, tp, agbp,
+							  ri->ri_pag);
 		rcur->bc_refc.nr_ops = nr_ops;
 		rcur->bc_refc.shape_changes = shape_changes;
 	}
-	*pcur = rcur;
 
 	switch (ri->ri_type) {
 	case XFS_REFCOUNT_INCREASE: