v4l2-event: Remove pending events from fh event queue when unsubscribing

Quoted 2 lines

This patch fixes these dangling pointers in the available queue by removing all matching pending events on unsubscription.

The idea is fine, but the implementation is inefficient.

Instead of the list_for_each_entry_safe you can just do:

	for (i = 0; i < sev->in_use; i++) {
		list_del(&sev->events[sev_pos(sev, i)].list);
		fh->navailable--;
	}

It's untested, but this should do the trick.