net: arc: Demote non-compliant kernel-doc headers

Fixes the following W=1 kernel build warning(s):

 drivers/net/ethernet/arc/emac_rockchip.c:18: warning: expecting prototype for emac(). Prototype was for DRV_NAME() instead
Signed-off-by: Yang Shen <shenyang39@huawei.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/arc/emac_rockchip.c

 // SPDX-License-Identifier: GPL-2.0-or-later
-/**
+/*
  * emac-rockchip.c - Rockchip EMAC specific glue layer
  *
  * Copyright (C) 2014 Romain Perier <romain.perier@gmail.com>