cpufreq: don't leave stale policy pointer in cdbs->cur_policy

Clear ->cur_policy when stopping a governor, or the ->cur_policy
pointer may be stale on systems with have_governor_per_policy when a
new policy is allocated due to CPU hotplug offline/online.

[rjw: Changelog]
Suggested-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Jacob Shin <jacob.shin@amd.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/cpufreq_governor.c

@@ -366,6 +366,7 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 
 		mutex_lock(&dbs_data->mutex);
 		mutex_destroy(&cpu_cdbs->timer_mutex);
+		cpu_cdbs->cur_policy = NULL;
 
 		mutex_unlock(&dbs_data->mutex);