ARM: sa1100/gpio: use new line value setter callbacks

struct gpio_chip now has callbacks for setting line values that return
an integer, allowing to indicate failures. Convert the driver to using
them.

Link: https://lore.kernel.org/r/20250407-gpiochip-set-rv-arm-v1-2-9e4a914c7fd4@linaro.org


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>