pinctrl: xway: statify xway_pinconf_group_set()

This function is not exported and is only used locally. Make it static.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Link: https://lore.kernel.org/20250612-gpiochip-set-rv-pinctrl-remaining-v1-7-556b0a530cd4@linaro.org


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>