kobject: should use kobject_put() in kset-example

We should call kobject_put() instead of kfree() if kobject_init_and_add()
returns an error, shouldn't we? Don't set up a bad example ;)

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>