ucm2: fix the external (headset) mic description
required kernel MR for this: https://source.puri.sm/Librem5/linux-next/-/merge_requests/540
Important: This is strictly speaking wrong with respect to detection: When headphones (not headset microphone) is plugged in, the "headset mic" device will be available.
Fixes #39 (closed)
Edited by Martin Kepplinger