lib/kobject.c : Remove redundant check in create_dir

create_dir is a static function used only in kobject_add_internal.
There's no need to do check here, for kobject_add_internal will
reject kobject with invalid name.

Signed-off-by: Yan Hong <clouds.yan@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>