net: pch_gbe: remove unneeded variable retval in __pch_gbe_suspend

Fix the following coccicheck warning:

./drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c:2415:5-11: Unneeded variable: "retval". Return "0" on line 2435

Reported-by: Tosk Robot <[e-mail]>
Signed-off-by: Kaixu Xia <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/oki-semi/pch_gbe/pch_gbe_main.c

···
 	struct pch_gbe_adapter *adapter = netdev_priv(netdev);
 	struct pch_gbe_hw *hw = &adapter->hw;
 	u32 wufc = adapter->wake_up_evt;
-	int retval = 0;
 
 	netif_device_detach(netdev);
 	if (netif_running(netdev))
···
 		pch_gbe_mac_set_wol_event(hw, wufc);
 		pci_disable_device(pdev);
 	}
-	return retval;
+	return 0;
 }
 
 #ifdef CONFIG_PM