passthrough/amd: avoid reading an uninitialized variable

passthrough/amd: avoid reading an uninitialized variable

update_intremap_entry_from_msi() doesn't write to its data pointer on
some error paths, so we copying that variable into the msg would count
as undefined behaviour.

Signed-off-by: Tim Deegan <tim@xen.org>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>