[SCSI] isci: fix needless ata reset escalations

isci is needlessly tying libata's hands by returning
SAM_STAT_CHECK_CONDITION to some ata errors.  Instead, prefer
SAS_PROTO_RESPONSE to let libata (via sas_ata_task_done()) disposition
the device-to-host fis.

For example isci is triggering an HSM Violation where AHCI is showing a
simple media error for the same bus condition:

isci:
ata7.00: failed command: READ VERIFY SECTOR(S)
ata7.00: cmd 40/00:01:00:00:00/00:00:00:00:00/e0 tag 0
         res 01/04:00:00:00:00/00:00:00:00:00/e0 Emask 0x3 (HSM violation)

ahci:
ata6.00: failed command: READ VERIFY SECTOR(S)
ata6.00: cmd 40/00:01:00:00:00/00:00:00:00:00/e0 tag 0
         res 51/40:01:00:00:00/00:00:00:00:00/e0 Emask 0x9 (media error)

Note that the isci response matches this from sas_ata_task_done():
	/* We saw a SAS error. Send a vague error. */
	[..]
	dev->sata_dev.fis[3] = 0x04; /* status err */
	dev->sata_dev.fis[2] = ATA_ERR;

The end effect is that isci is needlessly triggering hard resets when
they are not necessary.

Reported-by: Xun Ni <xun.ni@intel.com>
Tested-by: Nelson Cheng <nelson.cheng@intel.com>
Acked-by: Lukasz Dorau <lukasz.dorau@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>