mfd: ti_am335x_tscadc: Replace the header license text with SPDX tag

Drop the text license and replace it with an equivalent SPDX license tag
identifier.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20211015081506.933180-24-miquel.raynal@bootlin.com

include/linux/mfd/ti_am335x_tscadc.h

-#ifndef __LINUX_TI_AM335X_TSCADC_MFD_H
-#define __LINUX_TI_AM335X_TSCADC_MFD_H
-
+/* SPDX-License-Identifier: GPL-2.0-only */
 /*
  * TI Touch Screen / ADC MFD driver
  *
  * Copyright (C) 2012 Texas Instruments Incorporated - https://www.ti.com/
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License as
- * published by the Free Software Foundation version 2.
- *
- * This program is distributed "as is" WITHOUT ANY WARRANTY of any
- * kind, whether express or implied; without even the implied warranty
- * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
  */
 
+#ifndef __LINUX_TI_AM335X_TSCADC_MFD_H
+#define __LINUX_TI_AM335X_TSCADC_MFD_H
+
 #include <linux/mfd/core.h>
 
 #define REG_RAWIRQSTATUS	0x024