[SCSI] qlogicpti: fix sg list traversal error in continuation entries

The current sg list traversal logic for the continuation entries
doesn't advance the list pointer once all seven slots are used, so the
next continuation entry (if there is one) wrongly begins again at the
start of the sg list.

Fix by advancing the sg pointer after the for_each_sg().

Reported-by: Meelis Roos <mroos@ut.ee>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>