altos: Use AO_TICK_TYPE/AO_TICK_SIGNED for lco/pad code

altos: Use AO_TICK_TYPE/AO_TICK_SIGNED for lco/pad code

Was using 16-bit types, which 'mostly' worked, except that the pad
code compared ao_time() with a 16-bit value when determining the radio
status. After the box was on for 10 minutes (timer wrapped), the RF
timeout check would always fail, so the red LED would be lit.

Signed-off-by: Keith Packard <keithp@keithp.com>