IB/hfi1: Use free_netdev() in hfi1_netdev_free()

dummy_netdev shold be freed by free_netdev() instead of kfree(). Also
remove unneeded variable 'priv'

Fixes: 4730f4a6 ("IB/hfi1: Activate the dummy netdev")
Link: https://lore.kernel.org/r/20200602061635.31224-1-yuehaibing@huawei.comSigned-off-by: YueHaibing <yuehaibing@huawei.com>
Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/hfi1/netdev_rx.c

@@ -371,12 +371,9 @@ int hfi1_netdev_alloc(struct hfi1_devdata *dd)
 
 void hfi1_netdev_free(struct hfi1_devdata *dd)
 {
-	struct hfi1_netdev_priv *priv;
-
 	if (dd->dummy_netdev) {
-		priv = hfi1_netdev_priv(dd->dummy_netdev);
 		dd_dev_info(dd, "hfi1 netdev freed\n");
-		kfree(dd->dummy_netdev);
+		free_netdev(dd->dummy_netdev);
 		dd->dummy_netdev = NULL;
 	}
 }