ll_rw_blk: add io_context private pointer

To be used by as/cfq as they see fit.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 83dcd8c..a686eab 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -116,6 +116,7 @@
 
 	struct as_io_context *aic;
 	struct rb_root cic_root;
+	void *ioc_data;
 };
 
 void put_io_context(struct io_context *ioc);