pwm: raspberrypi-poe: 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/6758bcddb150f2c4353469937f1a68ecb87465ed.1707900770.git.u.kleine-koenig@pengutronix.deSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

drivers/pwm/pwm-raspberrypi-poe.c

@@ -122,7 +122,7 @@ static int raspberrypi_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	ret = raspberrypi_pwm_set_property(rpipwm->firmware, RPI_PWM_CUR_DUTY_REG,
 					   duty_cycle);
 	if (ret) {
-		dev_err(chip->dev, "Failed to set duty cycle: %pe\n",
+		dev_err(pwmchip_parent(chip), "Failed to set duty cycle: %pe\n",
 			ERR_PTR(ret));
 		return ret;
 	}