pwm: stm32-lp: 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/d79148ed49389c657b72df05758032be2b516ceb.1707900770.git.u.kleine-koenig@pengutronix.deSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

drivers/pwm/pwm-stm32-lp.c

@@ -61,7 +61,7 @@ static int stm32_pwm_lp_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	do_div(div, NSEC_PER_SEC);
 	if (!div) {
 		/* Clock is too slow to achieve requested period. */
-		dev_dbg(chip->dev, "Can't reach %llu ns\n", state->period);
+		dev_dbg(pwmchip_parent(chip), "Can't reach %llu ns\n", state->period);
 		return -EINVAL;
 	}
 
@@ -69,7 +69,7 @@ static int stm32_pwm_lp_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	while (div > STM32_LPTIM_MAX_ARR) {
 		presc++;
 		if ((1 << presc) > STM32_LPTIM_MAX_PRESCALER) {
-			dev_err(chip->dev, "max prescaler exceeded\n");
+			dev_err(pwmchip_parent(chip), "max prescaler exceeded\n");
 			return -EINVAL;
 		}
 		div = prd >> presc;
@@ -130,7 +130,7 @@ static int stm32_pwm_lp_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 				       (val & STM32_LPTIM_CMPOK_ARROK) == STM32_LPTIM_CMPOK_ARROK,
 				       100, 1000);
 	if (ret) {
-		dev_err(chip->dev, "ARR/CMP registers write issue\n");
+		dev_err(pwmchip_parent(chip), "ARR/CMP registers write issue\n");
 		goto err;
 	}
 	ret = regmap_write(priv->regmap, STM32_LPTIM_ICR,