drivers: visorbus: Use the correct style for SPDX License Identifier

This patch corrects the SPDX License Identifier style in
header file related to Unisys visorbus configuration.
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/20200419140017.GA7875@nishad
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/visorbus/controlvmchannel.h

@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2010 - 2015 UNISYS CORPORATION
  * All rights reserved.

drivers/visorbus/vbuschannel.h

@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2010 - 2015 UNISYS CORPORATION
  * All rights reserved.

drivers/visorbus/visorbus_private.h

@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2010 - 2015 UNISYS CORPORATION
  * All rights reserved.