ipmi: Remove all sysfs files on registration failure

In the Linux kernel, the following vulnerability has been resolved: ipmi: Remove all sysfs files on registration failure ipmi_add_smi() creates the nr_users and nr_msgs files before trying to create the maintenance_mode file. If that last creation fails, the error path removes only nr_users before dropping the final reference to the interface. Remove nr_msgs as well so no sysfs attribute embedded in the freed interface remains registered.