[SOUND] Sparc CS4231: Fix IRQ return value and initialization.

SBUS: Change IRQ-handler return value from 0 to IRQ_HANDLED and
fix some initialisation problems.

Change period_bytes_min from 4096 to 256 to allow driver to work with
low latency (VOIP) applications. Hope this does not break EBUS.

Signed-off-by: Georg Chini <georg.chini@triaton-webhosting.com>
Signed-off-by: David S. Miller <davem@davemloft.net>