staging: unisys: Fix NULL comparison vbusdeviceinfo.h

This patches resolves the NULL comparison checkpatch warnings

Signed-off-by: Erik Arfvidson <erik.arfvidson@unisys.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>