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/modules/px4iofirmware/registers.c

@@ -207,7 +207,7 @@ registers_set(uint8_t page, uint8_t offset, const uint16_t *values, unsigned num
 		/* Trigger all timer's channels in Oneshot mode to fire
 		 * the oneshots with updated values.
 		 */
-		up_pwm_update();
+		up_pwm_update(0xff);
 
 		break;