USB-Audio: Improve support for Focusrite 4th Gen devices

alsa-project/alsa-ucm-conf pull request #516 was opened from perexg:

There are 4 capture channels.

Request URL : https://github.com/alsa-project/alsa-ucm-conf/pull/516 Patch URL : https://github.com/alsa-project/alsa-ucm-conf/pull/516.patch Repository URL: https://github.com/alsa-project/alsa-ucm-conf