[pull requests] No SPDIF for Plantronics 3220, Dell AE515

[James Ettle]

Hello,

The Plantronics Blackwire 3220 Series headset and the Dell Professional 
Sound Bar AE515 are both USB-audio devices that show up with a digital 
S/PDIF output that physically doesn't exist.

This can be fixed by adding them to the USB-Audio.pcm.iec958_device list 
in USB-Audio.conf, with the following names:

    "DELL PROFESSIONAL SOUND BAR AE5"
    "Plantronics Blackwire 3220 Seri"

Patches for the respective devices are in the following alsa-lib pull 
requests:

   https://github.com/alsa-project/alsa-lib/pull/124
   https://github.com/alsa-project/alsa-lib/pull/126

Many thanks,
James.