drm/virtio: virtio_gpu_cmd_resource_create_3d: drop unused fence arg

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Robert Foss <robert.foss@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20181128151021.29565-3-kraxel@redhat.com