cpufreq: pass policy to __cpufreq_get()

There is no point finding out the 'policy' again within __cpufreq_get()
when all the callers already have it. Just make them pass policy instead.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>