Needed when VirtioPCIClass subclasses have their own
class struct with some extra fields.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-id: 20190307080244.9011-2-kraxel@redhat.com