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

This patch corrects the SPDX License Identifier style in
header files related to USB Miscellaneous 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 <[e-mail]>
Signed-off-by: Nishad Kamdar <[e-mail]>
Link: https://lore.kernel.org/r/20200404094638.GA5319@nishad
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/misc/sisusbvga/sisusb.h

···
-// SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause)
+/* SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause) */
 /*
  * sisusb - usb kernel driver for Net2280/SiS315 based USB2VGA dongles
  *

drivers/usb/misc/sisusbvga/sisusb_init.h

···
-// SPDX-License-Identifier: (GPL-2.0+ OR BSD-3-Clause)
+/* SPDX-License-Identifier: (GPL-2.0+ OR BSD-3-Clause) */
 /* $XFree86$ */
 /* $XdotOrg$ */
 /*

drivers/usb/misc/sisusbvga/sisusb_struct.h

···
-// SPDX-License-Identifier: (GPL-2.0+ OR BSD-3-Clause)
+/* SPDX-License-Identifier: (GPL-2.0+ OR BSD-3-Clause) */
 /*
  * General structure definitions for universal mode switching modules
  *

drivers/usb/misc/usb_u132.h

···
-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
 * Common Header File for the Elan Digital Systems U132 adapter
 * this file should be included by both the "ftdi-u132" and