Need to specify mmap_object operation here!

Not sure how I tested this before, or whether I just made this change
locally and forgot to commit it and then lost the change.

sys/external/bsd/drm2/dist/drm/via/via_drv.c

@@ -94,6 +94,8 @@ static struct drm_driver driver = {
 	.ioctls = via_ioctls,
 #ifndef __NetBSD__
 	.fops = &via_driver_fops,
+#else
+	.mmap_object = drm_mmap_object,
 #endif
 	.name = DRIVER_NAME,
 	.desc = DRIVER_DESC,