hdaa_pcmchannel_setup: do not advertise AC3 8+0

The rest of the sound system supports 7+1 maximum and is not aware of 8+0.

I believe that these messages are caused by 8+0:
kernel: feeder_init(0xfffff801f935d680) on feeder_matrix returned 22
kernel: pcm0: feeder_build_matrix(): can't add feeder_matrix