[SPARC] cs4231: Fix SBUS support in this driver.

From: Christopher Zimmermann <madroach@zakweb.de>

This patch enables SBus support for the cs4231 sound driver.
It is tested on an Ultra2. Capture and playback both work.
I experienced lags and crashes using certain threaded
players like ogg123 and mp3blaster, while the former is
lagging far more. This behavior may be specific to SMP
systems. It is reproducable using the dummy sound card
driver. Sox works flawlessly.

Setting up the calculation of ptr in snd_cs4231_playback_pointer 
was a bit strange. I got it to work by not incrementing the
[pc]_periods_sent counter when starting DMA the first time
in cs4231_dma_trigger. Therefore this dummy thing.

[ I did some minor cleanups -DaveM ]

Signed-off-by: David S. Miller <davem@davemloft.net>