pwm: atmel-tcb: 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.

Link: https://lore.kernel.org/r/463d43cab01f97f3c4247c63cc08e76aa15684c4.1707900770.git.u.kleine-koenig@pengutronix.deSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

drivers/pwm/pwm-atmel-tcb.c

@@ -327,7 +327,7 @@ static int atmel_tcb_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	if ((atcbpwm && atcbpwm->duty > 0 &&
 			atcbpwm->duty != atcbpwm->period) &&
 		(atcbpwm->div != i || atcbpwm->period != period)) {
-		dev_err(chip->dev,
+		dev_err(pwmchip_parent(chip),
 			"failed to configure period_ns: PWM group already configured with a different value\n");
 		return -EINVAL;
 	}