WIP: etes603 improvements

I could use some feedback from other users on the dcoffset change. I changed that to 0x35 while before it would be guessed in the one of the tune steps. For me that value works really well and the tuning always got me 0x31. But I'm not sure if other situations do really require a different value. Especially because my device outputs different values for what the original author of the driver thought could be firmware versions or something similar.

This merge request should fix #56 (closed).