staging: vt6655: dpc.h: Fix comment style of SPDX License Identifier

Modify comment style of SPDX License Identifier for header file type, as
per the license identifier syntax.
Signed-off-by: Madhumitha Prabakaran <madhumithabiw@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vt6655/dpc.h

-// SPDX-License-Identifier: GPL-2.0+
+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Copyright (c) 1996, 2003 VIA Networking Technologies, Inc.
  * All rights reserved.