ANDROID: cpufreq: arm_big_little: 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
bL_cpufreq_set_rate() returning 0.

Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Change-Id: I6fe98b7be9439fe46a44bbfb369ca169c3eb58dc
Signed-off-by: Chris Redpath <chris.redpath@arm.com>