clocksource/drivers/mips-gic-timer: Convert to SPDX identifier

The licensing text references explicitely the COPYING file in the kernel
base directory, which is clearly GPL version 2 only.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Serge Semin <fancer.lancer@gmail.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: linux-mips@vger.kernel.org
Acked-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://lore.kernel.org/r/20220510171254.529249404@linutronix.deSigned-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/mips-gic-timer.c

-/*
- * This file is subject to the terms and conditions of the GNU General Public
- * License.  See the file "COPYING" in the main directory of this archive
- * for more details.
- *
- * Copyright (C) 2012 MIPS Technologies, Inc.  All rights reserved.
- */
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2012 MIPS Technologies, Inc.  All rights reserved.
 
 #define pr_fmt(fmt) "mips-gic-timer: " fmt