enc28j60: Convert to use SPDX identifier

Reduce size of duplicated comments by switching to use SPDX identifier.

No functional change.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/microchip/enc28j60.c

+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Microchip ENC28J60 ethernet driver (MAC + PHY)
  *
@@ -5,11 +6,6 @@
  * Author: Claudio Lanconelli <lanconelli.claudio@eptar.com>
  * based on enc28j60.c written by David Anders for 2.4 kernel version
  *
- * 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.
- *
  * $Id: enc28j60.c,v 1.22 2007/12/20 10:47:01 claudio Exp $
  */