gpio: mpc8xxx: Add platform device to gpiochip->parent

Dear Linus Walleij,

In old kernels, some APIs still try to use parent->of_node from struct gpio_chip,
and it could be resulted in kernel panic because parent is NULL. Adding platform
device to gpiochip->parent can fix this problem.
Signed-off-by: Johnson Chen <johnsonch.chen@moxa.com>
Link: https://patchwork.kernel.org/patch/11234609
Link: https://lore.kernel.org/r/HK0PR01MB3521489269F76467DFD7843FFA450@HK0PR01MB3521.apcprd01.prod.exchangelabs.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-mpc8xxx.c

@@ -346,6 +346,7 @@ static int mpc8xxx_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	gc = &mpc8xxx_gc->gc;
+	gc->parent = &pdev->dev;
 
 	if (of_property_read_bool(np, "little-endian")) {
 		ret = bgpio_init(gc, &pdev->dev, 4,