drm/nouveau/acr: return error when registering LSF if ACR not supported

This fixes an oops on TU11x GPUs where SEC2 attempts to register its falcon,
and triggers a NULL-pointer deref because ACR isn't yet supported.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nvkm/subdev/acr/lsfw.c

@@ -58,8 +58,12 @@ struct nvkm_acr_lsfw *
 nvkm_acr_lsfw_add(const struct nvkm_acr_lsf_func *func, struct nvkm_acr *acr,
 		 struct nvkm_falcon *falcon, enum nvkm_acr_lsf_id id)
 {
-	struct nvkm_acr_lsfw *lsfw = nvkm_acr_lsfw_get(acr, id);
+	struct nvkm_acr_lsfw *lsfw;
+
+	if (!acr)
+		return ERR_PTR(-ENOSYS);
 
+	lsfw = nvkm_acr_lsfw_get(acr, id);
 	if (lsfw && lsfw->func) {
 		nvkm_error(&acr->subdev, "LSFW %d redefined\n", id);
 		return ERR_PTR(-EEXIST);