ieee1394: video1394: DMA fix

This together with the phys_to_virt fix in lib/swiotlb.c::swiotlb_sync_sg
fixes video1394 DMA on machines with DMA bounce buffers, especially Intel
x86-64 machines with > 3GB RAM.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: David Moore <dcm@acm.org>
Tested-by: Nicolas Turro <Nicolas.Turro@inrialpes.fr>