bcache: Convert bch_btree_insert() to bch_btree_map_leaf_nodes()

Last of the btree_map() conversions. Main visible effect is
bch_btree_insert() is no longer taking a struct btree_op as an argument
anymore - there's no fancy state machine stuff going on, it's just a
normal function.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
diff --git a/drivers/md/bcache/btree.h b/drivers/md/bcache/btree.h
index 6ff08be..8fc1e89 100644
--- a/drivers/md/bcache/btree.h
+++ b/drivers/md/bcache/btree.h
@@ -281,8 +281,8 @@
 
 int bch_btree_insert_check_key(struct btree *, struct btree_op *,
 			       struct bkey *);
-int bch_btree_insert(struct btree_op *, struct cache_set *,
-		     struct keylist *, atomic_t *, struct bkey *);
+int bch_btree_insert(struct cache_set *, struct keylist *,
+		     atomic_t *, struct bkey *);
 
 int bch_gc_thread_start(struct cache_set *);
 size_t bch_btree_gc_finish(struct cache_set *);