cpufreq: tegra20: Release clocks properly

Properly put requested clocks in the module init/exit code.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>