net: chelsio: cxgb4vf: Fix an error code in cxgb4vf_pci_probe()

During the process of driver probing, probe function should return < 0
for failure, otherwise kernel will treat value == 0 as success.

Therefore, we should set err to -EINVAL when
adapter->registered_device_map is NULL. Otherwise kernel will assume
that driver has been successfully probed and will cause unexpected
errors.
Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb4vf/cxgb4vf_main.c

@@ -3196,6 +3196,7 @@ static int cxgb4vf_pci_probe(struct pci_dev *pdev,
 	}
 	if (adapter->registered_device_map == 0) {
 		dev_err(&pdev->dev, "could not register any net devices\n");
+		err = -EINVAL;
 		goto err_disable_interrupts;
 	}