scsi: introduce a new result field in struct scsi_request

[hch at lst.de]

On Tue, Apr 18, 2017 at 10:34:20PM +0000, Bart Van Assche wrote:
> Did you perhaps intend "req->result" instead of "rq->result"?

Yes.

> Did you intend "war" or is that perhaps a typo?

I'll fix the comment.

> >  	trace_scsi_dispatch_cmd_done(cmd);
> > -	blk_mq_complete_request(cmd->request, cmd->request->errors);
> > +	blk_mq_complete_request(cmd->request, 0);
> >  }
> 
> Why has cmd->request->errors been changed into 0?

Because the argument is only used to set req->errors, which we won't
look at any more.