The cpufreq core supports the cpufreq_for_each_valid_entry macro
helper for iteration over the cpufreq_frequency_table, so use it.

It should have no functional changes.
Signed-off-by: NStratos Karafotis <stratosk@semaphore.gr>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>