cpufreq: cppc: Reorder code and remove apply_hisi_workaround variable

With the current approach we have an extra check in the
cppc_cpufreq_get_rate() callback, which checks if hisilicon's get rate
implementation should be used instead. While it works fine, the approach
isn't very straight forward, over that we have an extra check in the
routine.

Rearrange code and update the cpufreq driver's get() callback pointer
directly for the hisilicon case. This gets the extra variable is removed
and the extra check isn't required anymore as well.

Tested-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>