gpio: don't dereference gdev->chip in gpiochip_setup_dev()

We don't need to dereference gdev->chip in gpiochip_setup_dev() as at
the time it's called, the label in the associated struct gpio_device is
already set.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>