drm/nouveau/nvif: return null pointers on failure, in addition to ret != 0

Reported by Coverity.  The intention is that the return value is
checked, but let's be more paranoid and make it extremely obvious
if something forgets to.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nvif/notify.c

@@ -237,8 +237,10 @@ nvif_notify_new(struct nvif_object *object, int (*func)(struct nvif_notify *),
 	if (notify) {
 		int ret = nvif_notify_init(object, nvif_notify_del, func, work,
 					   type, data, size, reply, notify);
-		if (ret)
+		if (ret) {
 			kfree(notify);
+			notify = NULL;
+		}
 		*pnotify = notify;
 		return ret;
 	}

drivers/gpu/drm/nouveau/nvif/object.c

@@ -275,8 +275,10 @@ nvif_object_new(struct nvif_object *parent, u32 handle, u32 oclass,
 	if (object) {
 		int ret = nvif_object_init(parent, nvif_object_del, handle,
 					   oclass, data, size, object);
-		if (ret)
+		if (ret) {
 			kfree(object);
+			object = NULL;
+		}
 		*pobject = object;
 		return ret;
 	}