bcachefs: Fix trans_lock_write()

On failure to get a write lock (because we had a conflicting read lock),
we need to make sure to upgrade the read lock to an intent lock - or we
could end up spinning.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/btree_update_leaf.c

@@ -569,7 +569,8 @@ static inline bool have_conflicting_read_lock(struct btree_trans *trans, struct
 		//if (path == pos)
 		//	break;
 
-		if (path->nodes_locked != path->nodes_intent_locked)
+		if (path->nodes_locked != path->nodes_intent_locked &&
+		    !bch2_btree_path_upgrade(trans, path, path->level + 1))
 			return true;
 	}