batteryCheck: refine low battery reporting sevirity

To make sure QGC also shows a box and reads out for "low battery"
and make events and mavlink_log reports consistent.

Low - Critical
Critical - Critical
Emergency - Emergency

src/modules/commander/failsafe/framework.cpp

@@ -292,10 +292,9 @@ void FailsafeBase::notifyUser(uint8_t user_intended_mode, Action action, Action
 
 		if (action != Action::Warn) {
 			mavlink_log_critical(&_mavlink_log_pub, "Failsafe activated\t");
-		};
+		}
 	}
 
-
 #endif /* EMSCRIPTEN_BUILD */
 }