net: dsa: mv88e6060: Add SPDX header

Add an SPDX header, and remove the license text.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6060.c

+// SPDX-License-Identifier: GPL-2.0+
 /*
  * net/dsa/mv88e6060.c - Driver for Marvell 88e6060 switch chips
  * Copyright (c) 2008-2009 Marvell Semiconductor
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
  */
 
 #include <linux/delay.h>