gpio: of: simplify with scoped for each OF child loop

Use scoped for_each_xxx loop when iterating over device nodes to make
code a bit simpler.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240816151356.154991-1-krzysztof.kozlowski@linaro.org


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