igb: Cleanups to fix assignment in if error

This patch fixes ERROR:ASSIGN_IN_IF found with checkpatch file check.
Signed-off-by: Carolyn Wyborny <carolyn.wyborny@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb_main.c

@@ -4056,7 +4056,8 @@ static void igb_check_wvbr(struct igb_adapter *adapter)
 	switch (hw->mac.type) {
 	case e1000_82576:
 	case e1000_i350:
-		if (!(wvbr = rd32(E1000_WVBR)))
+		wvbr = rd32(E1000_WVBR);
+		if (!wvbr)
 			return;
 		break;
 	default: