ipmi: fix memleak when unload ipmi driver
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 3fa7cbdbe383c9322d68589d44f6fd6e2f6f51ec. For more details please see the references link.