ethtool: Fix an error code in cxgb2.c

When adapter->registered_device_map is NULL, the value of err is
uncertain, we set err to -EINVAL to avoid ambiguity.

Clean up smatch warning:
drivers/net/ethernet/chelsio/cxgb/cxgb2.c:1114 init_one() warn: missing
error code 'err'
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb/cxgb2.c

@@ -1111,6 +1111,7 @@ static int init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 	if (!adapter->registered_device_map) {
 		pr_err("%s: could not register any net devices\n",
 		       pci_name(pdev));
+		err = -EINVAL;
 		goto out_release_adapter_res;
 	}