POSIX baro SITL: Failed advert type is pointer, not number

src/platforms/posix/drivers/barosim/baro.cpp

@@ -278,7 +278,7 @@ BAROSIM::init()
 	_baro_topic = orb_advertise_multi(ORB_ID(sensor_baro), &brp,
 				&_orb_class_instance, (is_external()) ? ORB_PRIO_HIGH : ORB_PRIO_DEFAULT);
 
-	if (_baro_topic == (orb_advert_t)(-1)) {
+	if (_baro_topic == nullptr) {
 			PX4_ERR("failed to create sensor_baro publication");
 	}