cpufreq: Reorganize checks in cpufreq_offline()

Notice that cpufreq_offline() only needs to check policy_is_inactive()
once and rearrange the code in there to make that happen.

No expected functional impact.

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