pwm: cros-ec: Make use of pwmchip_parent() accessor

struct pwm_chip::dev is about to change. To not have to touch this
driver in the same commit as struct pwm_chip::dev, use the accessor
function provided for exactly this purpose.
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/486c40609bd9e339d7e5576e2501f63111b59b8b.1707900770.git.u.kleine-koenig@pengutronix.deSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

drivers/pwm/pwm-cros-ec.c

@@ -172,7 +172,7 @@ static int cros_ec_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
 
 	ret = cros_ec_pwm_get_duty(ec_pwm->ec, ec_pwm->use_pwm_type, pwm->hwpwm);
 	if (ret < 0) {
-		dev_err(chip->dev, "error getting initial duty: %d\n", ret);
+		dev_err(pwmchip_parent(chip), "error getting initial duty: %d\n", ret);
 		return ret;
 	}