AP_Baro_PX4: fixed baro driver to run at full rate

we were skipping samples due to a timer handling bug. It now checks
for new samples at 100Hz
AP_Compass_PX4: fixed handling of a saturated compass

a saturated compass is now marked unhealthy, rather than causing the
code to spin waiting for a valid sample. This fixes a problem with
strong magnets causing the main flight loop to stop