bcachefs: Add missing bch2_btree_node_iter_fix() call

Any time we're modifying what's in the btree, iterators potentially have
to be updated - this one was exposed by the reflink code.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_update_leaf.c

@@ -183,9 +183,8 @@ bool bch2_btree_bset_insert_key(struct btree_iter *iter,
 	clobber_u64s = 0;
 overwrite:
 	bch2_bset_insert(b, node_iter, k, insert, clobber_u64s);
-	if (k->u64s != clobber_u64s || bkey_whiteout(&insert->k))
-		bch2_btree_node_iter_fix(iter, b, node_iter, k,
-					 clobber_u64s, k->u64s);
+	bch2_btree_node_iter_fix(iter, b, node_iter, k,
+				 clobber_u64s, k->u64s);
 	bch2_btree_iter_verify(iter, b);
 	return true;
 }

fs/bcachefs/extents.c

@@ -1270,6 +1270,8 @@ static void __bch2_insert_fixup_extent(struct bch_fs *c,
 				btree_account_key_drop(l->b, _k);
 				_k->type = KEY_TYPE_discard;
 				reserve_whiteout(l->b, _k);
+				bch2_btree_node_iter_fix(iter, l->b, &l->iter,
+							_k, _k->u64s, _k->u64s);
 			}
 			break;
 		}