isdn: cpai: check ctr->cnr to avoid array index out of bound
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 by commit 1f3e2e97c003f80c4b087092b225c8787ff91e4d. For more details please see the references link.