Fix names of i2c busses

- The names of the i2c busses (i2c-x) are incorrect, so a user trying to
rely on pinout to tell what bus their device on will have trouble. The
hardware names are correct.
- Fetch the /dev/i2c-x names from sysfs

Change-Id: I30c77d3e845c0e460b2ed4f4c4a28e82041ee308