cpufreq: dt: invoke frequency-invariance setter function

Call the frequency-invariance setter function arch_set_freq_scale()
if the new frequency has been successfully set which is indicated by
dev_pm_opp_set_rate() returning 0.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>