dlm: init per node debugfs before add to node hash

Avoiding potential issues when a node is added to the hash but the
debugfs is not NULL or IS_ERR() so a potential iteration over the hash
and debugfs_remove() will not fail like in dlm_midcomms_exit().

However dlm_midcomms_exit() will be called in module init/exit function
and the hash should be empty anyway at those stages. We change the
behavior as cleanup to avoid potential issues.

Reported-by: Ginger <ginger.jzllee@gmail.com>
Closes: https://lore.kernel.org/gfs2/CAGp+u1ZE7UsQ4sSUHBKQXU8x3M_jwK=ek1urSjEtd3jXQGFmVg@mail.gmail.com
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>