pinctrl: mediatek: correct error handling

If no GPIO controller is found, the return value should not depend on a
random value on the stack. Initialize variable ret.

The problem was indicated by cppcheck.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Acked-by: Chunfeng Yun <chunfeng.yun@mediatek.com>

drivers/pinctrl/mediatek/pinctrl-mtk-common.c

@@ -615,6 +615,7 @@ static int mtk_gpiochip_register(struct udevice *parent)
 	if (!drv)
 		return -ENOENT;
 
+	ret = -ENOENT;
 	dev_for_each_subnode(node, parent)
 		if (ofnode_read_bool(node, "gpio-controller")) {
 			ret = 0;