xfs: fix sparse inodes 32-bit compile failure

The kbuild test robot reports the following compilation failure with a
32-bit kernel configuration:

	fs/built-in.o: In function `xfs_ifree_cluster':
	>> xfs_inode.c:(.text+0x17ac84): undefined reference to `__umoddi3'

This is due to the use of the modulus operator on a 64-bit variable in
the ASSERT() added as part of the following commit:

	xfs: skip unallocated regions of inode chunks in xfs_ifree_cluster()

This ASSERT() simply checks that the offset of the inode in a sparse
cluster is appropriately aligned. Since the maximum inode record offset
is 63 (for a 64 inode record) and the calculated offset here should be
something less than that, just use a 32-bit variable to store the offset
and call the do_mod() helper.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_inode.c

@@ -2248,6 +2248,7 @@ xfs_ifree_cluster(
 	int			inodes_per_cluster;
 	int			nbufs;
 	int			i, j;
+	int			ioffset;
 	xfs_daddr_t		blkno;
 	xfs_buf_t		*bp;
 	xfs_inode_t		*ip;
@@ -2268,9 +2269,9 @@ xfs_ifree_cluster(
 		 * physically allocated. Skip the cluster if an inode falls into
 		 * a sparse region.
 		 */
-		if ((xic->alloc & XFS_INOBT_MASK(inum - xic->first_ino)) == 0) {
-			ASSERT(((inum - xic->first_ino) %
-				inodes_per_cluster) == 0);
+		ioffset = inum - xic->first_ino;
+		if ((xic->alloc & XFS_INOBT_MASK(ioffset)) == 0) {
+			ASSERT(do_mod(ioffset, inodes_per_cluster) == 0);
 			continue;
 		}