scsi: fix fall out of sg-chaining patch in qlogicpti

Boaz writes:

"I've reviewed all patches since Matthew's, and I find one small
problem.

In the load_cmd() there is a compound loop where the first 4 sg's are
set then the rest are set into a memory structure in group of 7 sg's.

Well the second 7-group and on is a bug because sg pointer does not advance.
This is a fall out from Jens's patch."

The reporter, Meelis Roos <mroos@ut.ee>, verified that this patch
does indeed fix his problem with qlogicpti.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>