cpufreq: interactive_pro: Call cpufreq_get/put_global_kobject correctly

cpufreq_get/put_global_kobject() provides refcounting for
cpufreq_global_kobject. Users need to call these APIs if they intend
to use cpufreq_global_kobject.

Wrap cpufreq_global_kobject usage with get/put calls in interactive
governor.

Change-Id: I03c6830c297475a83c3eab723f1ec5449dcd151a
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>