cpufreq: tegra194: Staticize struct tegra_cpufreq_soc instances

Fix sparse warnings by marking these structures static.

Fixes: 273bc890 ("cpufreq: tegra194: Add support for Tegra234")
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Sumit Gupta <sumitg@nvidia.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>