gpiolib: acpi: make fwnode take precedence in struct gpio_chip

If the driver sets the fwnode in struct gpio_chip, let it take
precedence over the parent's fwnode.

This is a follow up to the commit 9126a738edc1 ("gpiolib: of: make
fwnode take precedence in struct gpio_chip").

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>