HiFIBerryOS bugfix for DSP boards

Unfortunately there was a bug in the latest HiFiBerryOS version which results in crashed in the UI and other problems when being used with our DSP cards.

We have prepared a bugfix release. It's not yet officially released as we would like to do more testing.

However, you can try by yourself already:
/opt/hifiberry/bin/update --experimental

This should fix the following bugs:
- no modification of DSP parameters possible
- no SPDIF input on DAC+ DSP (install DSP profile v14)
- GUI crashes