pwm: mtk-disp: 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/93ba7ef22f8d26f17e64326249d5da54ab8014ea.1707900770.git.u.kleine-koenig@pengutronix.deSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

drivers/pwm/pwm-mtk-disp.c

@@ -91,14 +91,14 @@ static int mtk_disp_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	if (!mdp->enabled) {
 		err = clk_prepare_enable(mdp->clk_main);
 		if (err < 0) {
-			dev_err(chip->dev, "Can't enable mdp->clk_main: %pe\n",
+			dev_err(pwmchip_parent(chip), "Can't enable mdp->clk_main: %pe\n",
 				ERR_PTR(err));
 			return err;
 		}
 
 		err = clk_prepare_enable(mdp->clk_mm);
 		if (err < 0) {
-			dev_err(chip->dev, "Can't enable mdp->clk_mm: %pe\n",
+			dev_err(pwmchip_parent(chip), "Can't enable mdp->clk_mm: %pe\n",
 				ERR_PTR(err));
 			clk_disable_unprepare(mdp->clk_main);
 			return err;
@@ -181,13 +181,13 @@ static int mtk_disp_pwm_get_state(struct pwm_chip *chip,
 
 	err = clk_prepare_enable(mdp->clk_main);
 	if (err < 0) {
-		dev_err(chip->dev, "Can't enable mdp->clk_main: %pe\n", ERR_PTR(err));
+		dev_err(pwmchip_parent(chip), "Can't enable mdp->clk_main: %pe\n", ERR_PTR(err));
 		return err;
 	}
 
 	err = clk_prepare_enable(mdp->clk_mm);
 	if (err < 0) {
-		dev_err(chip->dev, "Can't enable mdp->clk_mm: %pe\n", ERR_PTR(err));
+		dev_err(pwmchip_parent(chip), "Can't enable mdp->clk_mm: %pe\n", ERR_PTR(err));
 		clk_disable_unprepare(mdp->clk_main);
 		return err;
 	}