of: Constify struct device_node function arguments

Functions which don't change the refcount or otherwise modify struct
device_node can make struct device_node const.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20241010-dt-const-v1-3-87a51f558425@kernel.org


Signed-off-by: Rob Herring (Arm) <robh@kernel.org>