drm/tilcdc: panel: make better use of gpiod API

Since 39b2bbe3 (gpio: add flags argument to gpiod_get*() functions)
which appeared in v3.17-rc1, the gpiod_get* functions take an additional
parameter that allows to specify direction and initial value for output.

Furthermore there is devm_gpiod_get_optional which is designed to get
optional gpios.

Simplify driver accordingly.
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

drivers/gpu/drm/tilcdc/tilcdc_panel.c

@@ -375,24 +375,16 @@ static int panel_probe(struct platform_device *pdev)
 		dev_info(&pdev->dev, "found backlight\n");
 	}
 
-	panel_mod->enable_gpio = devm_gpiod_get(&pdev->dev, "enable");
+	panel_mod->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
+							 GPIOD_OUT_LOW);
 	if (IS_ERR(panel_mod->enable_gpio)) {
 		ret = PTR_ERR(panel_mod->enable_gpio);
-		if (ret != -ENOENT) {
 		dev_err(&pdev->dev, "failed to request enable GPIO\n");
 		goto fail_backlight;
 	}
 
-		/* Optional GPIO is not here, continue silently. */
-		panel_mod->enable_gpio = NULL;
-	} else {
-		ret = gpiod_direction_output(panel_mod->enable_gpio, 0);
-		if (ret < 0) {
-			dev_err(&pdev->dev, "failed to setup GPIO\n");
-			goto fail_backlight;
-		}
+	if (panel_mod->enable_gpio)
 		dev_info(&pdev->dev, "found enable GPIO\n");
-	}
 
 	mod = &panel_mod->base;
 	pdev->dev.platform_data = mod;