samples/kobject: Replace foo_ktype's default_attrs field with groups

The kobj_type default_attrs field is being replaced by the
default_groups field. Replace foo_ktype's default_attrs field with
default_groups and use the ATTRIBUTE_GROUPS macro to create
foo_default_groups.

This patch was tested by loading the kset-example module and verifying
that the sysfs files for the attributes in the default group were
created.

Signed-off-by: Kimberly Brown <kimbrownkd@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>