block: implement blk_rq_pos/[cur_]sectors() and convert obvious ones

Implement accessors - blk_rq_pos(), blk_rq_sectors() and
blk_rq_cur_sectors() which return rq->hard_sector, rq->hard_nr_sectors
and rq->hard_cur_sectors respectively and convert direct references of
the said fields to the accessors.

This is in preparation of request data length handling cleanup.

Geert	: suggested adding const to struct request * parameter to accessors
Sergei	: spotted error in patch description

[ Impact: cleanup ]

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Tested-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Ackec-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Cc: Borislav Petkov <petkovbb@googlemail.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/drivers/block/viodasd.c b/drivers/block/viodasd.c
index ecccf65..e821eed 100644
--- a/drivers/block/viodasd.c
+++ b/drivers/block/viodasd.c
@@ -368,12 +368,12 @@
 		blkdev_dequeue_request(req);
 		/* check that request contains a valid command */
 		if (!blk_fs_request(req)) {
-			viodasd_end_request(req, -EIO, req->hard_nr_sectors);
+			viodasd_end_request(req, -EIO, blk_rq_sectors(req));
 			continue;
 		}
 		/* Try sending the request */
 		if (send_request(req) != 0)
-			viodasd_end_request(req, -EIO, req->hard_nr_sectors);
+			viodasd_end_request(req, -EIO, blk_rq_sectors(req));
 	}
 }
 
@@ -590,7 +590,7 @@
 		err = vio_lookup_rc(viodasd_err_table, bevent->sub_result);
 		printk(VIOD_KERN_WARNING "read/write error %d:0x%04x (%s)\n",
 				event->xRc, bevent->sub_result, err->msg);
-		num_sect = req->hard_nr_sectors;
+		num_sect = blk_rq_sectors(req);
 	}
 	qlock = req->q->queue_lock;
 	spin_lock_irqsave(qlock, irq_flags);