ieee1394: sbp2: lower block queue alignment requirement

The old setting is copy & waste from usb-storage and doesn't apply to
sbp2.  There is only 4-byte alignment required for everything, except
for S/G table elements which have to be 8-byte aligned according to the
SBP-2 spec.  (They happen to be ____cacheline_aligned in our
implementation.  Whether that's good is another question.)

We now simply don't tune block queue alignment at all.  The default
alignment would surely never become anything else than a multiple of 4,
else tons of calls to blk_queue_dma_alignment would have to be added
everywhere in drivers/...

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>