cpufreq: Acquire the lock in cpufreq_policy_restore() for reading

In cpufreq_policy_restore() before system suspend policy is read from
percpu's cpufreq_cpu_data_fallback.  It's a read operation rather
than a write one, so take the lock for reading in there.
Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/cpufreq.c

@@ -906,11 +906,11 @@ static struct cpufreq_policy *cpufreq_policy_restore(unsigned int cpu)
 	struct cpufreq_policy *policy;
 	unsigned long flags;
 
-	write_lock_irqsave(&cpufreq_driver_lock, flags);
+	read_lock_irqsave(&cpufreq_driver_lock, flags);
 
 	policy = per_cpu(cpufreq_cpu_data_fallback, cpu);
 
-	write_unlock_irqrestore(&cpufreq_driver_lock, flags);
+	read_unlock_irqrestore(&cpufreq_driver_lock, flags);
 
 	return policy;
 }