cpufreq: Clean up cpufreq_parse_governor()

Drop an unnecessary local variable from cpufreq_parse_governor()
and rearrange the code in there to make it easier to follow.

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