s390-virtio: Rename machine class name to use MACHINE_TYPE_NAME

s390-virtio: Rename machine class name to use MACHINE_TYPE_NAME

Machine class names should use the "-machine" suffix to allow
class-name-based machine class lookup to work. Rename the s390-virtio
machine class using the MACHINE_TYPE_NAME macro.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>