asix-sigma: Only change number of channels after successful firmware upload

asix-sigma: Only change number of channels after successful firmware upload

The asix-sigma driver supports different samplerates, which will involve
different firmware images and will affect the number of available logic
channels as well as their memory layout in downloaded sample data.

Make sure to only store the configuration's parameters after the setup
of that configuration has successfully completed, and make sure to store
a consistent set of parameters. Specifically don't change the number of
channels when the firmware upload failed.

This fixes part of bug #471.

Suggested-By: Marian Cingel <redacted>