cpufreq: exit() callback is optional

The exit() callback is optional and shouldn't be called without checking
a valid pointer first.

Also, we must clear freq_table pointer even if the exit() callback isn't
present.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Fixes: 91a12e9 ("cpufreq: Allow light-weight tear down and bring up of CPUs")
Fixes: f339f35 ("cpufreq: Rearrange locking in cpufreq_remove_dev()")
Reported-by: Lizhe <sensor1010@163.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/cpufreq.c

@@ -1679,10 +1679,13 @@ static void __cpufreq_offline(unsigned int cpu, struct cpufreq_policy *policy)
 	 */
 	if (cpufreq_driver->offline) {
 		cpufreq_driver->offline(policy);
-	} else if (cpufreq_driver->exit) {
-		cpufreq_driver->exit(policy);
-		policy->freq_table = NULL;
+		return;
 	}
+
+	if (cpufreq_driver->exit)
+		cpufreq_driver->exit(policy);
+
+	policy->freq_table = NULL;
 }
 
 static int cpufreq_offline(unsigned int cpu)
@@ -1740,7 +1743,7 @@ static void cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif)
 	}
 
 	/* We did light-weight exit earlier, do full tear down now */
-	if (cpufreq_driver->offline)
+	if (cpufreq_driver->offline && cpufreq_driver->exit)
 		cpufreq_driver->exit(policy);
 
 	up_write(&policy->rwsem);