The TypeInfo incorrectly just lets the class size be inherited.  It won't
actually break things, since the class is abstract, but we should get it
right.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>