[ALSA] cs5535audio: drop unused bus master stuff

We really only care about the first two bus masters (playback and capture).
There's no need to have unused BM code lying around, so let's get rid of it.
If for some reason we trigger an IRQ for some BM that we're not using.. well,
that warrants spitting out an error message (imo).

Signed-off-by: Andres Salomon <dilinger@debian.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>