gfs2: Register fs after creating workqueues

Before this patch, the gfs2 file system was registered prior to creating
the three workqueues. In some cases this allowed dlm to send recovery
work to a workqueue that did not yet exist because gfs2 was still
initializing.

This patch changes the order of gfs2's initialization routine so it only
registers the file system after the work queues are created.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>