staging: bcm2835-audio: Drop debug messages in bcm2835-pcm.c
These debug messages worsen the code readability a lot while they give
little debuggability (which we already have via tracing, in anyway).
Let's clean them up. This allows us to reduce the
snd_bcm2835_pcm_lib_ioctl() function to be a direct call of the
snd_pcm_lib_ioctl callback (like most other drivers do), too.