bcachefs: set_btree_iter_dontneed also clears should_be_locked

This is part of a larger series cleaning up the semantics of
should_be_locked and adding assertions around it; if we don't need an
iterator/path anymore, it clearly doesn't need to be locked.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_iter.h

@@ -498,8 +498,13 @@ static inline void set_btree_iter_dontneed(struct btree_iter *iter)
 {
 	struct btree_trans *trans = iter->trans;
 
-	if (!trans->restarted)
-		btree_iter_path(trans, iter)->preserve = false;
+	if (!iter->path || trans->restarted)
+		return;
+
+	struct btree_path *path = btree_iter_path(trans, iter);
+	path->preserve		= false;
+	if (path->ref == 1)
+		path->should_be_locked	= false;
 }
 
 void *__bch2_trans_kmalloc(struct btree_trans *, size_t);