USB-Audio: fix comment in MOTU M4 config

alsa-project/alsa-ucm-conf pull request #379 was opened from davide125:

Mic2 is 2R, not 1R, so update the Stereo entry accordingly. This makes it consistent with the M2 and M6 (https://github.com/alsa-project/alsa-ucm-conf/pull/378) configs.

Request URL : https://github.com/alsa-project/alsa-ucm-conf/pull/379 Patch URL : https://github.com/alsa-project/alsa-ucm-conf/pull/379.patch Repository URL: https://github.com/alsa-project/alsa-ucm-conf