gpio: ixp4xx: Replace of_node_to_fwnode() with more suitable API

of_node_to_fwnode() is a IRQ domain specific implementation of
of_fwnode_handle(). Replace the former with more suitable API.

Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240822223332.705560-1-andy.shevchenko@gmail.com


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