USB: isp1760: Use the correct style for SPDX License Identifier

This patch corrects the SPDX License Identifier style in
header files related to ISP1760 USB host 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://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/20200404093803.GA4983@nishadSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/isp1760/isp1760-core.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Driver for the NXP ISP1760 chip
  *

drivers/usb/isp1760/isp1760-regs.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Driver for the NXP ISP1760 chip
  *

drivers/usb/isp1760/isp1760-udc.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Driver for the NXP ISP1761 device controller
  *