kobject: Comment and warning fixes to kobject.c

This dots some i's and crosses some t's after left over from when
kobject_kset_add_dir was built from kobject_add_dir. 

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>