bcachefs: Fix another iterator counting bug

We were marking the end of where we could insert incorrectly for
indirect extents.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/extent_update.c

@@ -76,7 +76,8 @@ static int count_iters_for_insert(struct btree_trans *trans,
 
 			if (*nr_iters >= max_iters) {
 				struct bpos pos = bkey_start_pos(k.k);
-				pos.offset += r_k.k->p.offset - idx;
+				pos.offset += min_t(u64, k.k->size,
+						    r_k.k->p.offset - idx);
 
 				*end = bpos_min(*end, pos);
 				ret = 1;