e1000e: Enclose e1000e_pm_thaw() with CONFIG_PM_SLEEP

Fix following compilation warning:
drivers/net/ethernet/intel/e1000e/netdev.c:6238:12: warning
‘e1000e_pm_thaw’ defined but not used [-Wunused-function]
 static int e1000e_pm_thaw(struct device *dev)
            ^
Signed-off-by: NHiroaki SHIMODA <shimoda.hiroaki@gmail.com>
Tested-by: NAaron Brown <aaron.f.brown@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/e1000e/netdev.c

@@ -6235,6 +6235,7 @@ static int __e1000_resume(struct pci_dev *pdev)
 	return 0;
 }
 
+#ifdef CONFIG_PM_SLEEP
 static int e1000e_pm_thaw(struct device *dev)
 {
 	struct net_device *netdev = pci_get_drvdata(to_pci_dev(dev));
@@ -6255,7 +6256,6 @@ static int e1000e_pm_thaw(struct device *dev)
 	return 0;
 }
 
-#ifdef CONFIG_PM_SLEEP
 static int e1000e_pm_suspend(struct device *dev)
 {
 	struct pci_dev *pdev = to_pci_dev(dev);