bcache: Btree verify code improvements

Used this fixed code to find and fix the bug fixed by
a4d885097b0ac0cd1337f171f2d4b83e946094d4.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
diff --git a/drivers/md/bcache/btree.h b/drivers/md/bcache/btree.h
index 12c99b1..580b011 100644
--- a/drivers/md/bcache/btree.h
+++ b/drivers/md/bcache/btree.h
@@ -292,7 +292,7 @@
 	(w ? up_write : up_read)(&b->lock);
 }
 
-void bch_btree_node_read(struct btree *);
+void bch_btree_node_read_done(struct btree *);
 void bch_btree_node_write(struct btree *, struct closure *);
 
 void bch_btree_set_root(struct btree *);