xfs: don't leak uuid table on rmmod

Don't leak the UUID table when the module is unloaded.
(Found with kmemleak.)

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>