pmdomain: core: constify of_phandle_args in add device and subdomain

Pointer to of_phandle_args is not modified by of_genpd_add_device() and
of_genpd_add_subdomain(), so it can be made pointer to const for code
safety and readability.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240208202822.631449-2-krzysztof.kozlowski@linaro.org


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>