cpuidle/powernv: staticise powernv_idle_driver

powernv_idle_driver isn't exported, it can be made static. Found by sparse.
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpuidle/cpuidle-powernv.c

@@ -22,7 +22,7 @@
 
 #define POWERNV_THRESHOLD_LATENCY_NS 200000
 
-struct cpuidle_driver powernv_idle_driver = {
+static struct cpuidle_driver powernv_idle_driver = {
 	.name             = "powernv_idle",
 	.owner            = THIS_MODULE,
 };