cpufreq: qcom-hw: invoke frequency-invariance setter function

Add calls to arch_set_freq_scale() in qcom-cpufreq-hw driver to enable
frequency invariance.

Signed-off-by: Douglas RAILLARD <douglas.raillard@arm.com>
Reviewed-by: Quentin Perret <quentin.perret@arm.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>