drm/i915: constify pointers to hwmon_channel_info

Statically allocated array of pointers to hwmon_channel_info can be made
const for safety.

Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230511175446.282041-1-krzysztof.kozlowski@linaro.org