tty: serial: Use the correct style for SPDX License Identifier

This patch corrects the SPDX License Identifier style in
header files related to tty serial drivers.
For C header files Documentation/process/license-rules.rst
mandates C-like comments (opposed to C source files where
C++ style should be used).

Changes made by using a script provided by Joe Perches here:
https://lkml.org/lkml/2019/2/7/46.
Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Nishad Kamdar <nishadkamdar@gmail.com>
Link: https://lore.kernel.org/r/20200301204517.GA10368@nishadSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  *  Driver for 8250/16550-type serial ports
  *

drivers/tty/serial/8250/8250_dwlib.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /* Synopsys DesignWare 8250 library header file. */
 
 #include <linux/types.h>

drivers/tty/serial/atmel_serial.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * include/linux/atmel_serial.h
  *

drivers/tty/serial/cpm_uart/cpm_uart.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  *  Driver for CPM (SCC/SMC) serial ports
  *

drivers/tty/serial/icom.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * icom.h
  *

drivers/tty/serial/ifx6x60.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /****************************************************************************
  *
  * Driver for the IFX spi modem.

drivers/tty/serial/jsm/jsm.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /************************************************************************
  * Copyright 2003 Digi International (www.digi.com)
  *

drivers/tty/serial/pic32_uart.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * PIC32 Integrated Serial Driver.
  *

drivers/tty/serial/serial_mctrl_gpio.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Helpers for controlling modem lines via GPIO
  *

drivers/tty/serial/sirfsoc_uart.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Drivers for CSR SiRFprimaII onboard UARTs.
  *

drivers/tty/serial/stm32-usart.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) Maxime Coquelin 2015
  * Copyright (C) STMicroelectronics SA 2017

drivers/tty/serial/timbuart.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * timbuart.c timberdale FPGA GPIO driver
  * Copyright (c) 2009 Intel Corporation