kobject: fix kset sample error path

Previously, example_init() leaked a kset if any of the object creations
failed.  This fixes the leak by calling kset_unregister() in the error
path.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>