fix pwm: only update oneshot timers owned by the current pwm_out instance

This fixes the case where oneshot was enabled with multi-instance pwm_out,
triggering oneshot updates too close to each other and as a result could
lead to spinning motors while disarmed.

src/drivers/drv_pwm_output.h

@@ -358,7 +358,7 @@ __EXPORT extern int	up_pwm_servo_set_rate_group_update(unsigned group, unsigned
  * Nothing is done if not in oneshot mode.
  *
  */
-__EXPORT extern void up_pwm_update(void);
+__EXPORT extern void up_pwm_update(unsigned channel_mask);
 
 /**
  * Set the current output value for a channel.

src/drivers/pwm_out/PWMOut.cpp

@@ -438,7 +438,7 @@ bool PWMOut::updateOutputs(bool stop_motors, uint16_t outputs[MAX_ACTUATORS],
 	 * the oneshots with updated values.
 	 */
 	if (num_control_groups_updated > 0) {
-		up_pwm_update(); // TODO: review for multi
+		up_pwm_update(_pwm_mask);
 	}
 
 	return true;