xfs: fix two memory leaks in xfs_attr_list.c error paths

This plugs 2 trivial leaks in xfs_attr_shortform_list and
xfs_attr3_leaf_list_int.

Signed-off-by: Mateusz Guzik <mguzik@redhat.com>
Cc: <stable@vger.kernel.org>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>