cpufreq: qcom-nvmem: fix compilation warning for qcom_cpufreq_ipq806x_match_list

cpufreq: qcom-nvmem: fix compilation warning for qcom_cpufreq_ipq806x_match_list

If CONFIG_OF is not enabled, of_match_node() is set as NULL and
qcom_cpufreq_ipq806x_match_list won't be used causing a compilation
warning.

Flag qcom_cpufreq_ipq806x_match_list as __maybe_unused to fix the
compilation warning.

While at it also flag as __initconst as it's used only in probe contest
and can be freed after probe.

This follows the pattern of the usual of_device_id variables.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202511202119.6zvvFMup-lkp@intel.com/
Fixes: 58f5d39d5ed8 ("cpufreq: qcom-nvmem: add compatible fallback for ipq806x for no SMEM")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
[ Viresh: Drop __initconst ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>