drm/nouveau/disp: fix oops in destructor with headless cards

If init doesn't run then disp->outp might not be initialized, resulting
in an oops.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/core/engine/disp/base.c

@@ -99,9 +99,11 @@ _nouveau_disp_dtor(struct nouveau_object *object)
 
 	nouveau_event_destroy(&disp->vblank);
 
+	if (disp->outp.next) {
 		list_for_each_entry_safe(outp, outt, &disp->outp, head) {
 			nouveau_object_ref(NULL, (struct nouveau_object **)&outp);
 		}
+	}
 
 	nouveau_engine_destroy(&disp->base);
 }