bcachefs: node scan: ignore multiple nodes with same seq if interior

Interior nodes are not really needed, when we have to scan - but if this
pops up for leaf nodes we'll need a real heuristic.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_node_scan.c

@@ -302,6 +302,8 @@ static int handle_overwrites(struct bch_fs *c,
 
 			start->max_key = bpos_predecessor(n->min_key);
 			start->range_updated = true;
+		} else if (n->level) {
+			n->overwritten = true;
 		} else {
 			struct printbuf buf = PRINTBUF;