cpufreq: tegra: fix the wrong clock name

The "cpu" and "pclk_p_cclk" was a virtual clock name that was used in
the legacy Tegra clock framework. It was not used after converting to
CCF. Fix it as the correct clock name that we are using.

Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Joseph Lo <josephl@nvidia.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>