gpiolib: Check array_info for NULL only once in gpiod_get_array()

gpiod_get_array() has a long if-else-if branching where each of them
tests for the same variable to be not NULL. Instead, check for NULL
before even going to that flow.

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