dlm: Fix dlm lock status block comment in dlm.h

There is only one place in the dlm where the sb_status is set
and that is queue_cast(). Tracing back the callers of that
function shows that the listed set of return values is
out of date, so here are an updated set.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>