envy24control: fix control callback for spdif output

[GitHub pull_request - opened <github@xxxxxxxxxxxxxxxx>]

alsa-project/alsa-tools pull request #30 was opened from andreas56:

Update S/PDIF Output Settings GUI when settings change.

Request URL   : https://github.com/alsa-project/alsa-tools/pull/30
Patch URL     : https://github.com/alsa-project/alsa-tools/pull/30.patch
Repository URL: https://github.com/alsa-project/alsa-tools