[ALSA] sun-cs4231: code improvements

This patch does some code improvements to make
driver (both code and binary) shorter.
It also make use of card->private_data pointer to
store chip information.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>