fs: dlm: cleanup lock order

This patch cleanups the lock order to hold at first the close_lock and
then held the nodes_srcu read lock. Probably it will never be a problem
as nodes_srcu is only a read lock preventing the node pointer getting
freed.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>