staging: unisys: fix up some SPDX tags

One .h file was missing a SPDX tag, and another one was wrong after
looking at the text of the license itself, so fix both of these issues
up at the same time.

Cc: David Kershner <david.kershner@unisys.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/unisys/include/iochannel.h

-// SPDX-License-Identifier: GPL-2.0
+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Copyright (C) 2010 - 2016 UNISYS CORPORATION
  * All rights reserved.

drivers/staging/unisys/include/visorchannel.h

+// SPDX-License-Identifier: GPL-2.0+
 /*
  * Copyright (C) 2010 - 2013 UNISYS CORPORATION
  * All rights reserved.