nel cannot
handle 32 bit DMA with this device.  Problem manifests as noise when
using more than 2GB of RAM, possibly only on 64 bit machines.

The OSS driver actually uses a 29 bit DMA mask for both devices, this
seems like overkill for now.

Signed-off-by: Lee Revell <rlrevell@joe-job.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>