mlx4_en: Fix cleanup if workqueue create in mlx4_en_add() fails

If creating a workqueue fails, don't jump to the error path where that
same workqueue is destroyed, since destroy_workqueue() can't handle a
NULL pointer.

This was spotted by the Coverity checker (CID 2617).
Signed-off-by: NRoland Dreier <rolandd@cisco.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/mlx4/en_main.c

@@ -181,7 +181,7 @@ static void *mlx4_en_add(struct mlx4_dev *dev)
 	mdev->workqueue = create_singlethread_workqueue("mlx4_en");
 	if (!mdev->workqueue) {
 		err = -ENOMEM;
-		goto err_close_nic;
+		goto err_mr;
 	}
 
 	/* At this stage all non-port specific tasks are complete:
@@ -214,9 +214,8 @@ static void *mlx4_en_add(struct mlx4_dev *dev)
 	flush_workqueue(mdev->workqueue);
 
 	/* Stop event queue before we drop down to release shared SW state */
-
-err_close_nic:
 	destroy_workqueue(mdev->workqueue);
+
 err_mr:
 	mlx4_mr_free(dev, &mdev->mr);
 err_uar: