perf: Ensure swevent hrtimer is properly destroyed

In the Linux kernel, the following vulnerability has been resolved:

perf: Ensure swevent hrtimer is properly destroyed

With the change to hrtimer_try_to_cancel() in

perf_swevent_cancel_hrtimer() it appears possible for the hrtimer to

still be active by the time the event gets freed.

Make sure the event does a full hrtimer_cancel() on the free path by

installing a perf_event::destroy handler.