dlm: fix plock invalid read
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v5.15.46 by commit acdad5bc9827922ec2f2e84fd198718aa8e8ab92, it was introduced in version v2.6.22 by commit 586759f03e2e9031ac5589912a51a909ed53c30a. For more details please see the references link.