Print out the offset at which the error occured.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20200108090348.21224-3-clg@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>