USB: chipidea: Use the correct style for SPDX License Identifier

This patch corrects the SPDX License Identifier style in
header files related to ChipIdea Highspeed Dual Role Controller.
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://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.org%2Flkml%2F2019%2F2%2F7%2F46&data=02%7C01%7CPeter.Chen%40nxp.com%7Cbea69ff84b574ca6b48e08d7c8cf58cf%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637198665199494622&sdata=bk1n4%2BvnrfRS6ZDrps%2BuXiImdzaxKZ00YskBg6pjtn4%3D&reserved=0.
Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Nishad Kamdar <nishadkamdar@gmail.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>

drivers/usb/chipidea/bits.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * bits.h - register bits of the ChipIdea USB IP core
  *

drivers/usb/chipidea/ci.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * ci.h - common structures, functions, and macros of the ChipIdea driver
  *

drivers/usb/chipidea/ci_hdrc_imx.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Copyright 2012 Freescale Semiconductor, Inc.
  */

drivers/usb/chipidea/otg.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2013-2014 Freescale Semiconductor, Inc.
  *

drivers/usb/chipidea/otg_fsm.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2014 Freescale Semiconductor, Inc.
  *

drivers/usb/chipidea/udc.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * udc.h - ChipIdea UDC structures
  *