dlm: uninitialized variable on error in dlm_listen_for_all()

The "sock" variable is not initialized on this error path.

Cc: stable@vger.kernel.org
Fixes: 2dc6b115

 ("fs: dlm: introduce generic listen")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>