bcache: Kill op->cl

This isn't used for waiting asynchronously anymore - so this is a fairly
trivial refactoring.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
diff --git a/drivers/md/bcache/bset.c b/drivers/md/bcache/bset.c
index fae5b7b..f7b5525 100644
--- a/drivers/md/bcache/bset.c
+++ b/drivers/md/bcache/bset.c
@@ -1196,7 +1196,7 @@
 	int ret;
 
 	memset(&t, 0, sizeof(struct bset_stats));
-	bch_btree_op_init_stack(&t.op);
+	bch_btree_op_init(&t.op, -1);
 
 	ret = bch_btree_map_nodes(&t.op, c, &ZERO_KEY, btree_bset_stats);
 	if (ret < 0)