audio: Improve snd_receive type-safety
audio: Improve snd_receive type-safety

We can pass it a SndChannel rather than an opaque void* data pointer
which we then blindly cast.
This came to light through a -Wshadow warning as there was a local
variable 'data' in addition to the 'data' parameter.

fgouget/spice,fgouget/spice,SPICE/spice,fgouget/spice,fgouget/spice,SPICE/spice,SPICE/spice