This enables continuous mode for the HMC5883 instead of single
measurement mode, therefore working around a ADSP crash.

This code is flyable, but a few problems exist which cause values in the .config files to be overwritten by the defaults in the .XML file.

Original description:
Modified the sensor module to prevent the selection of an invalid
secondary/tertiary gyro if the primary gyro times out

Not sure why they got removed in the first place in the merge.
I also don't know how they are used and what they are for, comments
welcome.