fixup bcachefs: Use for_each_btree_key_upto() more consistently

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/io.c

@@ -217,7 +217,8 @@ int bch2_sum_sector_overwrites(struct btree_trans *trans,
 
 	bch2_trans_copy_iter(&iter, extent_iter);
 
-	for_each_btree_key_continue_norestart(iter, BTREE_ITER_SLOTS, old, ret) {
+	for_each_btree_key_upto_continue_norestart(iter,
+				new->k.p, BTREE_ITER_SLOTS, old, ret) {
 		s64 sectors = min(new->k.p.offset, old.k->p.offset) -
 			max(bkey_start_offset(&new->k),
 			    bkey_start_offset(old.k));