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>