xen/xenbus: Rename the variable xen_store_mfn to xen_store_gfn
xen/xenbus: Rename the variable xen_store_mfn to xen_store_gfn

The variable xen_store_mfn is effectively storing a GFN and not an MFN.

Signed-off-by: Julien Grall <2fe41d4e32b0bb991f63b975f2bed08c1e666665@citrix.com>
Signed-off-by: David Vrabel <b9d45bd1f671e508cd8daa63dfc3cabb597562df@citrix.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs