MIPS: ralink: Switch pinmux.h to SPDX header

The original license text had a typo ("publishhed") which would be
likely to confuse automated licensing auditing tools. Let's just switch
to SPDX instead of fixing the wording.
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

arch/mips/include/asm/mach-ralink/pinmux.h

+// SPDX-License-Identifier: GPL-2.0
 /*
- *  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
- *  publishhed by the Free Software Foundation.
- *
  *  Copyright (C) 2012 John Crispin <john@phrozen.org>
  */