driver/px4io: set default failsafe values

src/drivers/px4io/px4io.cpp

@@ -803,6 +803,14 @@ void PX4IO::update_params()
 						int32_t pwm_fail_new = _mixing_output.failsafeValue(i);
 						param_set(param_find(str), &pwm_fail_new);
 					}
+
+				} else {
+					if (pwm_default_channel_mask & 1 << i) {
+						_mixing_output.failsafeValue(i) = PWM_MOTOR_OFF;
+
+					} else {
+						_mixing_output.failsafeValue(i) = PWM_SERVO_STOP;
+					}
 				}
 			}
 		}