[DLM] fix reference counting

This is a fix for the patch

021d2ff3a08019260a1dc002793c92d6bf18afb6

I left off a dlm_hold_rsb which causes the box to panic if you try to use
debugfs.  This patch fixes the problem.  Sorry about that,

Signed-off-by: Josef Bacik <jwhiter@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>