dlm: add missing -ENOMEM if alloc_workqueue() fails

This patch sets an missing -ENOMEM as error return value when the
allocation of the dlm workqueue fails.

Fixes: 94e180d6 ("dlm: async freeing of lockspace resources")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202408110800.OsoP8TB9-lkp@intel.com/


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