sof-soundwire: use the ${find-device} lookup for the dmic device

alsa-project/alsa-ucm-conf pull request #77 was opened from perexg:

The PCM device number for the internal digital microphone is not fixed.

Request URL : https://github.com/alsa-project/alsa-ucm-conf/pull/77 Patch URL : https://github.com/alsa-project/alsa-ucm-conf/pull/77.patch Repository URL: https://github.com/alsa-project/alsa-ucm-conf