VT-d: make remap_entry_to_msi_msg() return consistent message

VT-d: make remap_entry_to_msi_msg() return consistent message

During debugging of another problem I found that in x2APIC mode, the
destination field of the low address value wasn't passed back
correctly. While this is benign in most cases (as the value isn't being
used anywhere), it can be confusing (and misguiding) when printing the
value read or when comparing it to the one previously passed into the
inverse function.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>