Due to commit cdda911c evdev only
becomes readable when the buffer contains an EV_SYN/SYN_REPORT event.

So in order to read the tablet sensor data as it happens we need to
ensure that we always call input_sync() after input_report_switch()
Signed-off-by: Carlos Alberto Lopez Perez <clopez@igalia.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>