dm cache: Fix UAF in destroy()

dm cache: Fix UAF in destroy()

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 v4.9.337 by commit 034cbc8d3b47a56acd89453c29632a9c117de09d, it was introduced in version v3.9 by commit c6b4fcbad044e6fffcc75bba160e720eb8d67d17. For more details please see the references link.