fs: dlm: fix building without lockdep

This patch uses assert_spin_locked() instead of lockdep_is_held()
where it's available to use because lockdep_is_held() is only available
if CONFIG_LOCKDEP is set.

In other cases like lockdep_sock_is_held() we surround it by a
CONFIG_LOCKDEP idef.

Fixes: dbb751ff ("fs: dlm: parallelize lowcomms socket handling")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>