Staging: unisys: Fix noderef sparse warnings in vbusdeviceinfo.h

vbuschannel_devinfo_to_string() was declared with the devinfo argument
as a pointer to __iomem space.  No callers of this function need the
__iomem space, so I removed that constraint.

Same thing goes for vbuschannel_sanitize_buffer().  It doesn't need to
operate on I/O space.

Signed-off-by: Ken Cox <jkc@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>