xfs: convert RUI log formats to use variable length arrays

Use variable length array declarations for RUI log items,
and replace the open coded sizeof formulae with a single function.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index fd6be45..3409753 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1782,9 +1782,8 @@
 	if (!xfs_rud_zone)
 		goto out_destroy_icreate_zone;
 
-	xfs_rui_zone = kmem_zone_init((sizeof(struct xfs_rui_log_item) +
-			((XFS_RUI_MAX_FAST_EXTENTS - 1) *
-				sizeof(struct xfs_map_extent))),
+	xfs_rui_zone = kmem_zone_init(
+			xfs_rui_log_item_sizeof(XFS_RUI_MAX_FAST_EXTENTS),
 			"xfs_rui_item");
 	if (!xfs_rui_zone)
 		goto out_destroy_rud_zone;