The invalid state isn't any different from a hole, so merge the two
states.  Use the more descriptive hole name, but keep it as the first
value of the enum to catch uninitialized fields.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>