i40iw: Add missing check for interface already open

In i40iw_open(), check if interface is already open
and return success if it is.

Fixes: 8e06af71 ("i40iw: add main, hdr, status")
Reported-by: NStefan Assmann <sassmann@redhat.com>
Signed-off-by: NMustafa Ismail <mustafa.ismail@intel.com>
Signed-off-by: NShiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: NDoug Ledford <dledford@redhat.com>

drivers/infiniband/hw/i40iw/i40iw_main.c

@@ -1558,6 +1558,10 @@ static int i40iw_open(struct i40e_info *ldev, struct i40e_client *client)
 	enum i40iw_status_code status;
 	struct i40iw_handler *hdl;
 
+	hdl = i40iw_find_netdev(ldev->netdev);
+	if (hdl)
+		return 0;
+
 	hdl = kzalloc(sizeof(*hdl), GFP_KERNEL);
 	if (!hdl)
 		return -ENOMEM;