Fix for issue: 3.15.6 - error compiling pcm512 sound drivers #641 

This is a fix for the compilation problems with the IQaudIO sound card and pcm512x driver in 3.15

The issue arose because the original commit (in 3.10) to add the IQaudIO sound card support included the pcm512x driver. However, it is already present in 3.15 which resulted in a mix of the old and new drivers.