isdn: mISDN: Fix sleeping function called from invalid context

isdn: mISDN: Fix sleeping function called from invalid context

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 v5.4.156 by commit 4054b869dc263228d30a4755800b78f0f2ba0c89. For more details please see the references link.