The callers of object_initialize_child() commonly  pass either
&child, sizeof(child), or pchild, sizeof(*pchild).  Tidy up the few
that don't, mostly to keep the next commit simpler.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20200610053247.1583243-36-armbru@redhat.com>