intel_idle: Clean up NULL pointer check in intel_idle_init()

Instead of comparing intel_idle_cpuidle_devices with NULL apply
the "!" (not) operator to it when checking it against NULL.

No intentional functional impact.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/idle/intel_idle.c

@@ -1630,7 +1630,7 @@ static int __init intel_idle_init(void)
 		 boot_cpu_data.x86_model);
 
 	intel_idle_cpuidle_devices = alloc_percpu(struct cpuidle_device);
-	if (intel_idle_cpuidle_devices == NULL)
+	if (!intel_idle_cpuidle_devices)
 		return -ENOMEM;
 
 	intel_idle_cpuidle_driver_init();