cpufreq: powernv: Fix frame-size-overflow in powernv_cpufreq_reboot_notifier

The patch avoids allocating cpufreq_policy on stack hence fixing frame
size overflow in 'powernv_cpufreq_reboot_notifier':

  drivers/cpufreq/powernv-cpufreq.c: In function powernv_cpufreq_reboot_notifier:
  drivers/cpufreq/powernv-cpufreq.c:906:1: error: the frame size of 2064 bytes is larger than 2048 bytes

Fixes: cf30af76 ("cpufreq: powernv: Set the cpus to nominal frequency during reboot/kexec")
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Reviewed-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200922080254.41497-1-srikar@linux.vnet.ibm.com

drivers/cpufreq/powernv-cpufreq.c

@@ -885,12 +885,15 @@ static int powernv_cpufreq_reboot_notifier(struct notifier_block *nb,
 				unsigned long action, void *unused)
 {
 	int cpu;
-	struct cpufreq_policy cpu_policy;
+	struct cpufreq_policy *cpu_policy;
 
 	rebooting = true;
 	for_each_online_cpu(cpu) {
-		cpufreq_get_policy(&cpu_policy, cpu);
-		powernv_cpufreq_target_index(&cpu_policy, get_nominal_index());
+		cpu_policy = cpufreq_cpu_get(cpu);
+		if (!cpu_policy)
+			continue;
+		powernv_cpufreq_target_index(cpu_policy, get_nominal_index());
+		cpufreq_cpu_put(cpu_policy);
 	}
 
 	return NOTIFY_DONE;