block: Use accessor functions for queue limits

Convert all external users of queue limits to using wrapper functions
instead of poking the request queue variables directly.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index 8681b70..89bd438 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -3983,8 +3983,8 @@
 		return -ENODEV;
 	}
 
-	i = min(SDp->request_queue->max_hw_segments,
-		SDp->request_queue->max_phys_segments);
+	i = min(queue_max_hw_segments(SDp->request_queue),
+		queue_max_phys_segments(SDp->request_queue));
 	if (st_max_sg_segs < i)
 		i = st_max_sg_segs;
 	buffer = new_tape_buffer((SDp->host)->unchecked_isa_dma, i);