Sensors: ensure trigger param is present

src/modules/sensors/sensors.cpp

@@ -631,6 +631,7 @@ Sensors::Sensors() :
 	(void)param_find("PWM_AUX_MIN");
 	(void)param_find("PWM_AUX_MAX");
 	(void)param_find("PWM_AUX_DISARMED");
+	(void)param_find("TRIG_MODE");
 	
 	/* fetch initial parameter values */
 	parameters_update();