cxgb3: fix 2 ports 1G regression

commit 88045b3c
	cxgb3: fix mac index mapping

	Override the mac index computation for the gen2 adapter,
	as each port is expected to use index 0.

introduces a regression on 2 port 1G adapter
as its xauicfg vpd value is null.
Add a check on the device id.
Signed-off-by: NDivy Le Ray <divy@chelsio.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/cxgb3/t3_hw.c

@@ -3692,8 +3692,12 @@ static void mc7_prep(struct adapter *adapter, struct mc7 *mc7,
 
 void mac_prep(struct cmac *mac, struct adapter *adapter, int index)
 {
+	u16 devid;
+
 	mac->adapter = adapter;
-	if (!adapter->params.vpd.xauicfg[1])
+	pci_read_config_word(adapter->pdev, 0x2, &devid);
+
+	if (devid == 0x37 && !adapter->params.vpd.xauicfg[1])
 		index = 0;
 	mac->offset = (XGMAC0_1_BASE_ADDR - XGMAC0_0_BASE_ADDR) * index;
 	mac->nucast = 1;