Cube blue incompatible with IST8308 compass (Ardupilot)

I think this PR will fix it:

Here is a 4.0.7 copter build with that patch applied for you to test:
http://uav.tridgell.net/tmp/copter-4-0.7-CubeBlack-IST8308-test1.apj
please comment on the PR when you have tested so we can confirm if it works.
Cheers, Tridge