net: sun: cassini: Cleanup license conflict

The recent addition of SPDX license identifiers to the files in
drivers/net/ethernet/sun created a licensing conflict.

The cassini driver files contain a proper license notice:

  * 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.

but the SPDX change added:

   SPDX-License-Identifier: GPL-2.0

So the file got tagged GPL v2 only while in fact it is licensed under GPL
v2 or later.

It's nice that people care about the SPDX tags, but they need to be more
careful about it. Not everything under (the) sun belongs to ...

Fix up the SPDX identifier and remove the boiler plate text as it is
redundant.

Fixes: c861ef83 ("sun: Add SPDX license tags to Sun network drivers")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Shannon Nelson <shannon.nelson@oracle.com>
Cc: Zhu Yanjun <yanjun.zhu@oracle.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Cc: stable@vger.kernel.org
Acked-by: Shannon Nelson <shannon.lee.nelson@gmail.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>