hmp: drop Error pointer indirection in hmp_handle_error

hmp: drop Error pointer indirection in hmp_handle_error

We don't need Error **, as all callers pass local Error object, which
isn't used after the call. Use Error * instead.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20191205174635.18758-5-vsementsov@virtuozzo.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>