cpufreq: Consolidate cpufreq_update_current_freq() and __cpufreq_get()

cpufreq: Consolidate cpufreq_update_current_freq() and __cpufreq_get()

Their implementations are quite similar, so modify
cpufreq_update_current_freq() somewhat and call it from
__cpufreq_get().

Also rename cpufreq_update_current_freq() to
cpufreq_verify_current_freq(), as that's what it is doing.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
[ rjw: Subject & changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>