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/6758bcd[e-mail]
Signed-off-by: Uwe Kleine-König <[e-mail]>

drivers/pwm/pwm-raspberrypi-poe.c

···
 	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;
 	}