USB Audio: Xonar U7 MKII needs `iec958_device` entry

alsa-project/alsa-lib issue #100 was opened from ndl:

`USB-Audio.conf` includes V1 of Asus Xonar U7 card but not [MKII version](https://www.asus.com/ch-en/Sound-Cards/Xonar-U7-MKII/), the section `USB-Audio.pcm.iec958_device` should be extended to include the string

"Xonar U7 MKII" 1

without this S/PDIF output doesn't work.

Issue URL : https://github.com/alsa-project/alsa-lib/issues/100 Repository URL: https://github.com/alsa-project/alsa-lib