gpio: ath79: Update the copyright notice

Add myself to the copyright list and remove the reference to Atheros'
BSP as nothing is left of this code.
Signed-off-by: Alban Bedel <albeu@free.fr>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-ath79.c

 /*
  *  Atheros AR71XX/AR724X/AR913X GPIO API support
  *
+ *  Copyright (C) 2015 Alban Bedel <albeu@free.fr>
  *  Copyright (C) 2010-2011 Jaiganesh Narayanan <jnarayanan@atheros.com>
  *  Copyright (C) 2008-2011 Gabor Juhos <juhosg@openwrt.org>
  *  Copyright (C) 2008 Imre Kaloz <kaloz@openwrt.org>
  *
- *  Parts of this file are based on Atheros' 2.6.15/2.6.31 BSP
- *
  *  This program is free software; you can redistribute it and/or modify it
  *  under the terms of the GNU General Public License version 2 as published
  *  by the Free Software Foundation.