ieee1394: iso and async streams: s/g list fix

Torsten Kaiser wrote:
> Looking that calltrace upwards, it seems replacing the
> memset(dma->sglist,...) with sg_init_table(...) would fix the BUG_ON()
> as that inits the SG_MAGIC.

Tested-by: Torsten Kaiser <just.for.lkml@googlemail.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>