octeon_ep: Fix error code in probe()

Set the error code if octep_ctrl_net_get_mtu() fails.  Currently the code
returns success.

Fixes: 0a5f853 ("octeon_ep: get max rx packet length from firmware")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Sathesh B Edara <sedara@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/octeon_ep/octep_main.c

@@ -1387,6 +1387,7 @@ static int octep_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 	if (max_rx_pktlen < 0) {
 		dev_err(&octep_dev->pdev->dev,
 			"Failed to get max receive packet size; err = %d\n", max_rx_pktlen);
+		err = max_rx_pktlen;
 		goto register_dev_err;
 	}
 	netdev->min_mtu = OCTEP_MIN_MTU;