w1: omap-hdq: add SPDX tag

Replace GPLv2 license text with SPDX and drop unnecessary file name in
comment to fix checkpatch warnings:

  WARNING: Missing or malformed SPDX-License-Identifier tag in line 1
  WARNING: It's generally not useful to have the filename in the file
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230415104304.104134-14-krzysztof.kozlowski@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/w1/masters/omap_hdq.c

+// SPDX-License-Identifier: GPL-2.0-only
 /*
- * drivers/w1/masters/omap_hdq.c
- *
  * Copyright (C) 2007,2012 Texas Instruments, Inc.
- *
- * This file is licensed under the terms of the GNU General Public License
- * version 2. This program is licensed "as is" without any warranty of any
- * kind, whether express or implied.
- *
  */
 #include <linux/kernel.h>
 #include <linux/module.h>