syslog, kern.log, messages are filled

running copter 3.7 dev:

Ardupilot seems to be filling up the disk with log messages in /var/log/kern.log /var/log/syslog and /var/log/messages.

Most of the messages are like the following.
```
[ 481.993933] rcio spi1.0: rcio_pwm: requested update on 1 to 50
[ 481.994056] rcio spi1.0: rcio_pwm: requested update on 2 to 50
[ 481.996450] rcio spi1.0: rcio_pwm: requested update on 0 to 490
[ 481.996592] rcio spi1.0: rcio_pwm: requested update on 0 to 490
```

About hundred of theses are logged every second and over the course of a couple hours it fills a 32 gigabyte sd card.

Reproduce the issue on Copter 3.7 dev and monitor /var/log/kern.log, /var/log/syslog, and /var/log/messages for repeated rcio_pwm entries. Trace the source of these messages and verify that normal operation no longer fills the SD card with hundreds of entries per second.

Written by the indexing model from the issue text.