qdev_print_props() receives and throws away Error objects just to
check for object_property_get_str() and object_property_print()
failure.  Unnecessary, both return suitable values, so use those
instead.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200707160613.848843-46-armbru@redhat.com>