pwm: cros-ec: Refuse requests with unsupported polarity

The driver only supports normal polarity and so should refuse requests
for inversed polarity.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-cros-ec.c

@@ -124,6 +124,9 @@ static int cros_ec_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	if (state->period != EC_PWM_MAX_DUTY)
 		return -EINVAL;
 
+	if (state->polarity != PWM_POLARITY_NORMAL)
+		return -EINVAL;
+
 	/*
 	 * EC doesn't separate the concept of duty cycle and enabled, but
 	 * kernel does. Translate.