gpio: gpiolib: fix confusing indention

There's a confusing indention in gpiochip_add_data_with_key(), which
could be misinterpreted on a quick walkthrough. Fixing this in order
to improve code readability a bit.
Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>