xtensa: ISS: add comment about etherdev freeing

iss_net_configure explicitly frees etherdev in all error return paths
except one where register_netdevice fails. In that remaining error
return path the etherdev is freed by the iss_net_pdev_release callback
triggered by the platform_device_unregister call. Add a comment stating
that.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/platforms/iss/network.c

@@ -540,6 +540,7 @@ static void iss_net_configure(int index, char *init)
 		rtnl_unlock();
 		pr_err("%s: error registering net device!\n", dev->name);
 		platform_device_unregister(&lp->pdev);
+		/* dev is freed by the iss_net_pdev_release callback */
 		return;
 	}
 	rtnl_unlock();