CVE-2021-46979

In the Linux kernel, the following vulnerability has been resolved: iio:
core: fix ioctl handlers removal Currently ioctl handlers are removed
twice. For the first time during iio_device_unregister() then later on
inside iio_device_unregister_eventset() and
iio_buffers_free_sysfs_and_mask(). Double free leads to kernel panic. Fix
this by not touching ioctl handlers list directly but rather letting code
responsible for registration call the matching cleanup routine itself.