drm/omap: tpd12s015: fix error handling

tpd12s015 driver is missing error value handling for gpio
initialization, causing 0 to be returned as an error if gpiod_get_*
fails. This may cause deferred probing to fail.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/gpu/drm/omapdrm/displays/encoder-tpd12s015.c

@@ -234,25 +234,30 @@ static int tpd_probe(struct platform_device *pdev)
 	if (r)
 		return r;
 
-
 	gpio = devm_gpiod_get_index_optional(&pdev->dev, NULL, 0,
 		 GPIOD_OUT_LOW);
-	if (IS_ERR(gpio))
+	if (IS_ERR(gpio)) {
+		r = PTR_ERR(gpio);
 		goto err_gpio;
+	}
 
 	ddata->ct_cp_hpd_gpio = gpio;
 
 	gpio = devm_gpiod_get_index_optional(&pdev->dev, NULL, 1,
 		 GPIOD_OUT_LOW);
-	if (IS_ERR(gpio))
+	if (IS_ERR(gpio)) {
+		r = PTR_ERR(gpio);
 		goto err_gpio;
+	}
 
 	ddata->ls_oe_gpio = gpio;
 
 	gpio = devm_gpiod_get_index(&pdev->dev, NULL, 2,
 		GPIOD_IN);
-	if (IS_ERR(gpio))
+	if (IS_ERR(gpio)) {
+		r = PTR_ERR(gpio);
 		goto err_gpio;
+	}
 
 	ddata->hpd_gpio = gpio;