dlm: fix invalid cluster name warning

dlm: fix invalid cluster name warning

BugLink: https://bugs.launchpad.net/bugs/1857158
[ Upstream commit 3595c559326d0b660bb088a88e22e0ca630a0e35 ]

The warning added in commit 3b0e761ba83
  "dlm: print log message when cluster name is not set"

did not account for the fact that lockspaces created
from userland do not supply a cluster name, so bogus
warnings are printed every time a userland lockspace
is created.

Signed-off-by: David Teigland <teigland@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>