Staging: vt6655-6: potential NULL dereference in hostap_disable_hostapd()

commit cb4855b4 upstream.

We fixed this to use free_netdev() instead of kfree() but unfortunately
free_netdev() doesn't accept NULL pointers.  Smatch complains about
this, it's not something I discovered through testing.

Fixes: 3030d40b ('staging: vt6655: use free_netdev instead of kfree')
Fixes: 0a438d5b ('staging: vt6656: use free_netdev instead of kfree')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[wt: only vt6656 was converted to free_netdev in 3.10]
Signed-off-by: Willy Tarreau <w@1wt.eu>

drivers/staging/vt6656/hostap.c

@@ -133,7 +133,8 @@ static int hostap_disable_hostapd(struct vnt_private *pDevice, int rtnl_locked)
             DBG_PRT(MSG_LEVEL_DEBUG, KERN_INFO "%s: Netdevice %s unregistered\n",
 		       pDevice->dev->name, pDevice->apdev->name);
 	}
-	free_netdev(pDevice->apdev);
+	if (pDevice->apdev)
+		free_netdev(pDevice->apdev);
 	pDevice->apdev = NULL;
     pDevice->bEnable8021x = false;
     pDevice->bEnableHostWEP = false;