cpufreq/intel_pstate: Replace synchronize_sched() with synchronize_rcu()

Now that synchronize_rcu() waits for preempt-disable regions of code
as well as RCU read-side critical sections, synchronize_sched() can be
replaced by synchronize_rcu().  This commit therefore makes this change.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: Len Brown <lenb@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: <linux-pm@vger.kernel.org>

drivers/cpufreq/intel_pstate.c

@@ -1930,7 +1930,7 @@ static void intel_pstate_clear_update_util_hook(unsigned int cpu)
 
 	cpufreq_remove_update_util_hook(cpu);
 	cpu_data->update_util_set = false;
-	synchronize_sched();
+	synchronize_rcu();
 }
 
 static int intel_pstate_get_max_freq(struct cpudata *cpu)