gpio: mmio: use new GPIO line value setter callbacks

gpio: mmio: use new GPIO 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.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250610-gpiochip-set-rv-gpio-v1-1-3a9a3c1472ff@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>