ocfs2: Fix userspace ABI breakage in sysfs

The userspace ABI of ocfs2's internal cluster stack (o2cb) was broken by
commit c60b7178 "kset: convert ocfs2 to
use kset_create".  Specifically, the '/sys/o2cb' kset was moved to
'/sys/fs/o2cb'.  This breaks all ocfs2 tools and renders the
filesystem unmountable.

This fix moves '/sys/o2cb' back where it belongs.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>