input: paw32xx: only reschedule the handler if motion is asserted

The motion event handler is currently setup to always retrigger until
there's no more motion data from the sensor. Change that to only
retrigger if the motion pin is asserted when the handler has finished
running, this saves a bunch of unnecessary spi transactions.

Ideally this driver would use a level interrupt, but I'd rather avoid
that as that is unsupported by many gpio controllers.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>