gpiolib: Move gpiochip_get_data() higher in the code

Move gpiochip_get_data() higher in the code as a preparation
for further refactoring.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
[Bartosz: tweak the commit message]
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>