terminal: discard async read() errors for evdev

terminal: discard async read() errors for evdev

If read() fails on evdev devices, we deal with this in idev_evdev_hup().
It is very likely this is an async revoke, therefore, we must not abort.
Fix our io helper to discard such errors after passing them to
idev_evdev_hup(), so we don't bail out of the event loop.