cpufreq: pcc-cpufreq: Mark sometimes used ID structs as __maybe_unused

Not used when MODULE is not defined.

Fixes the following W=1 kernel build warning(s):

 drivers/cpufreq/pcc-cpufreq.c:619:36: warning: ‘processor_device_ids’ defined but not used [-Wunused-const-variable=]
 619 | static const struct acpi_device_id processor_device_ids[] = {
 | ^~~~~~~~~~~~~~~~~~~~
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/pcc-cpufreq.c

@@ -616,7 +616,7 @@ static void __exit pcc_cpufreq_exit(void)
 	free_percpu(pcc_cpu_info);
 }
 
-static const struct acpi_device_id processor_device_ids[] = {
+static const struct acpi_device_id __maybe_unused processor_device_ids[] = {
 	{ACPI_PROCESSOR_OBJECT_HID, },
 	{ACPI_PROCESSOR_DEVICE_HID, },
 	{},