powerpc: 44x/gpio: use new line value setter callbacks

powerpc: 44x/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.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250502-gpiochip-set-rv-powerpc-v2-3-488e43e325bf@linaro.org