[SCSI] sas_ata: Implement sas_task_abort for ATA devices

ATA devices need special handling for sas_task_abort.  If the ATA command
came from SCSI, then we merely need to tell SCSI to abort the scsi_cmnd.
However, internal commands require a bit more work--we need to fill the qc
with the appropriate error status and complete the command, and eventually
post_internal will issue the actual ABORT TASK.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>