bcachefs: Fix lookup_first_inode() when inode_generations are present

This function is used for finding the hash seed (which is the same in
all versions of an inode in different snapshots): ff an inode has been
deleted in a child snapshot we need to iterate until we find a live
version.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/fsck.c

@@ -77,21 +77,17 @@ static int lookup_first_inode(struct btree_trans *trans, u64 inode_nr,
 	struct bkey_s_c k;
 	int ret;
 
-	bch2_trans_iter_init(trans, &iter, BTREE_ID_inodes,
-			     POS(0, inode_nr),
-			     BTREE_ITER_all_snapshots);
-	k = bch2_btree_iter_peek(&iter);
-	ret = bkey_err(k);
-	if (ret)
-		goto err;
-
-	if (!k.k || !bkey_eq(k.k->p, POS(0, inode_nr))) {
-		ret = -BCH_ERR_ENOENT_inode;
-		goto err;
+	for_each_btree_key_norestart(trans, iter, BTREE_ID_inodes, POS(0, inode_nr),
+				     BTREE_ITER_all_snapshots, k, ret) {
+		if (k.k->p.offset != inode_nr)
+			break;
+		if (!bkey_is_inode(k.k))
+			continue;
+		ret = bch2_inode_unpack(k, inode);
+		goto found;
 	}
-
-	ret = bch2_inode_unpack(k, inode);
-err:
+	ret = -BCH_ERR_ENOENT_inode;
+found:
 	bch_err_msg(trans->c, ret, "fetching inode %llu", inode_nr);
 	bch2_trans_iter_exit(trans, &iter);
 	return ret;