[SCSI] isci: fix event-get pointer increment

Hardware only increments the put pointer on event types >= 4.  Do not
increment the get pointer for event type 3.

Reported-by: Kapil Karkra <kapil.karkra@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>