stream-endpoint: add break to avoid implicit fallthrough

No functional change

stream-endpoint.c:172:3: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]

src/stream-endpoint.c

@@ -169,6 +169,7 @@ static int stream_set_active(struct stream *stream, bool active)
 			default:
 				break;
 			}
+			break;
 		default:
 			break;
 		}