direct.conf fails to work if DirectCardName is not specified

[GitHub issues - opened <github@xxxxxxxxxxxxxxxx>]

alsa-project/alsa-ucm-conf issue #183 was opened from brndd:

The following error is produced when a card uses direct.conf but DirectCardName is not specified (with e.g. `Define { DirectCardName "UMC204HD" }`

```
$ spa-acp-tool -c 1 -vvvv info
variable '${var:DirectCardName}' is not defined in this context!
```

Issue URL     : https://github.com/alsa-project/alsa-ucm-conf/issues/183
Repository URL: https://github.com/alsa-project/alsa-ucm-conf