iommu: constify of_phandle_args in xlate

The xlate callbacks are supposed to translate of_phandle_args to proper
provider without modifying the of_phandle_args.  Make the argument
pointer to const for code safety and readability.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240216144027.185959-2-krzysztof.kozlowski@linaro.org


Signed-off-by: Joerg Roedel <jroedel@suse.de>