gpiolib: Access device's fwnode via dev_fwnode()

GPIO device's fwnode should be accessed via dev_fwnode().
Make sure that gpiochip_setup_dev() follows that.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>