Staging: hv: osd.h: fix GUID reference problem

As GUID was a typedef, it hid the fact that we were passing it
a 2 variables in functions.  This fixes this up by passing it
as a pointer, as it should be.

Cc: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>