staging: vt6656: Use the correct style for SPDX license Identifier

This patch corrects the style for SPDX license Identifier in mac.h
by using "/* */" in place of "//" as per Linux kernel licensing rules.
Issue found by checkpatch.
Signed-off-by: Nishad Kamdar <nishadkamdar@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vt6656/mac.h

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