drm/virtio: Use lockless gem BO free callback

No dev->struct_mutex anywhere to be seen.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: David Airlie <airlied@linux.ie>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1464630800-30786-18-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/virtio/virtgpu_drv.c

@@ -143,7 +143,7 @@ static struct drm_driver driver = {
 	.gem_prime_vunmap = virtgpu_gem_prime_vunmap,
 	.gem_prime_mmap = virtgpu_gem_prime_mmap,
 
-	.gem_free_object = virtio_gpu_gem_free_object,
+	.gem_free_object_unlocked = virtio_gpu_gem_free_object,
 	.gem_open_object = virtio_gpu_gem_object_open,
 	.gem_close_object = virtio_gpu_gem_object_close,
 	.fops = &virtio_gpu_driver_fops,