drbd: fix in_flight rw indexing

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

drivers/block/drbd/drbd_req.c

@@ -40,7 +40,7 @@ static void _drbd_start_io_acct(struct drbd_conf *mdev, struct drbd_request *req
 	part_stat_inc(cpu, &mdev->vdisk->part0, ios[rw]);
 	part_stat_add(cpu, &mdev->vdisk->part0, sectors[rw], bio_sectors(bio));
 	part_stat_unlock();
-	mdev->vdisk->part0.in_flight++;
+	mdev->vdisk->part0.in_flight[rw]++;
 }
 
 /* Update disk stats when completing request upwards */
@@ -53,7 +53,7 @@ static void _drbd_end_io_acct(struct drbd_conf *mdev, struct drbd_request *req)
 	part_stat_add(cpu, &mdev->vdisk->part0, ticks[rw], duration);
 	part_round_stats(cpu, &mdev->vdisk->part0);
 	part_stat_unlock();
-	mdev->vdisk->part0.in_flight--;
+	mdev->vdisk->part0.in_flight[rw]--;
 }
 
 static void _req_is_done(struct drbd_conf *mdev, struct drbd_request *req, const int rw)