Please follow the steps mentioned here, to make sure FlytOS communicates with Pixhawk.
Also look at this APM documentation about TeraRanger, to understand how to configure APM for TeraRanger. They seem to use I2C directly connected to Pixhawk instead of using an Odroid for this.
In case you still want to use USB to connect TeraRanger with Odroid, you need to use this ros driver, which would publish TeraRanger output to rostopics, and then publish to mavros’s distance sensor topic. This topic is currently not available for APM, but available for PX4. We are in the process of fixing this bug.