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/systemcmds/pwm/pwm.cpp

@@ -701,7 +701,7 @@ pwm_main(int argc, char *argv[])
 			 * the oneshots with updated values.
 			 */
 
-			up_pwm_update();
+			up_pwm_update(0xff);
 #endif
 		}
 		rv = 0;