net: stmmac: Fix an error code in probe()

The function should return an error if create_singlethread_workqueue()
fails.

Fixes: 34877a15 ("net: stmmac: Rework and fix TX Timeout code")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -4250,6 +4250,7 @@ int stmmac_dvr_probe(struct device *device,
 	priv->wq = create_singlethread_workqueue("stmmac_wq");
 	if (!priv->wq) {
 		dev_err(priv->device, "failed to create workqueue\n");
+		ret = -ENOMEM;
 		goto error_wq;
 	}