dac960: switch to seq_file

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Yang Hongyang <yanghy@cn.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>