[SCSI] isci: Remove redundant isci_request.ttype field.

Use the existing IREQ_TMF flag as a request type indicator.

Signed-off-by: Jeff Skirvin <jeffrey.d.skirvin@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>