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

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

 drivers/net/phy/adin.c:3: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/net/phy/rockchip.c:3: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst

Cc: Heiner Kallweit <hkallweit1@gmail.com>
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Yang Shen <shenyang39@huawei.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/adin.c

 // SPDX-License-Identifier: GPL-2.0+
-/**
+/*
  *  Driver for Analog Devices Industrial Ethernet PHYs
  *
  * Copyright 2019 Analog Devices Inc.

drivers/net/phy/rockchip.c

 // SPDX-License-Identifier: GPL-2.0+
-/**
+/*
  * drivers/net/phy/rockchip.c
  *
  * Driver for ROCKCHIP Ethernet PHYs