Documentation: gpio: Fix return type of gpiod_set_raw_array_value*()

The return type of gpiod_set_raw_array_value() and
gpiod_set_raw_array_value_cansleep() was changed from void to int, but
the doc update was forgotten.

Fixes: 3027743f ("gpio: Remove VLA from gpiolib")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>