staging/lustre/obdclass: fix class_procfs_init error return value

Dan Carpenter noticed that procfs conversion patches introduced
a bug where should kobject_create_and_add, an error is not returned
from class_procfs_init.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>