fix documentation after renaming gpiod_set_array to gpiod_set_array_value

Patch "gpiolib: rename gpiod_set_array to gpiod_set_array_value" omitted
to also change the function names in the documentation. Let's fix that.

Signed-off-by: Rojhalat Ibrahim <imr@rtschenk.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>