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>