hwspinlock/sirf: Switch to SPDX license identifier

Use the appropriate SPDX license identifier in the CSR's SIRF hardware
spinlock driver source file and drop the previous boilerplate license text.

Cc: Wei Chen <wei.chen@csr.com>
Cc: Barry Song <baohua@kernel.org>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/hwspinlock/sirf_hwspinlock.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * SIRF hardware spinlock driver
  *
  * Copyright (c) 2015 Cambridge Silicon Radio Limited, a CSR plc group company.
- *
- * Licensed under GPLv2.
  */
 
 #include <linux/kernel.h>