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/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 3de0695..123003a 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -3741,6 +3741,7 @@
 		ret->nr_batch_requests = 0; /* because this is 0 */
 		ret->aic = NULL;
 		ret->cic_root.rb_node = NULL;
+		ret->ioc_data = NULL;
 		/* make sure set_task_ioprio() sees the settings above */
 		smp_wmb();
 		tsk->io_context = ret;