cpufreq: intel_pstate: Use locking in intel_cpufreq_verify_policy()

Race conditions are possible if intel_cpufreq_verify_policy()
is executed in parallel with global limits updates from sysfs,
so the invocation of intel_pstate_update_perf_limits() in it
should be carried out under intel_pstate_limits_lock.

Make that happen.
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: NSrinivas Pandruvada <srinivas.pandruvada@linux.intel.com>

drivers/cpufreq/intel_pstate.c

@@ -2103,8 +2103,12 @@ static int intel_cpufreq_verify_policy(struct cpufreq_policy *policy)
 	if (per_cpu_limits)
 		perf_limits = cpu->perf_limits;
 
+	mutex_lock(&intel_pstate_limits_lock);
+
 	intel_pstate_update_perf_limits(policy, perf_limits);
 
+	mutex_unlock(&intel_pstate_limits_lock);
+
 	return 0;
 }