[SCSI] isci: fix sata response handling

A bug (likely copy/paste) that has been carried from the original
implementation.  The unsolicited frame handling structure returns the
d2h fis in the isci_request.stp.rsp buffer.

Cc: <stable@kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>