fsck.ubifs: rebuild_fs: Add valid nodes into file

fsck.ubifs: rebuild_fs: Add valid nodes into file

This is the 3/12 step of rebuilding. Generate file according to left valid
inode nodes and dentry nodes. Based on the results from step 2, it is easy
to understand:

Step 2 has done:
 valid_inos - del_inos = left_inos
 valid_dents - del_dents = left_dents
Step 3 should do:
 Traverse left_inos and left_dents, insert inode/dentry nodes into
 corresponding file.

After that, all files are generated by scanning, the next thing to do is
dropping invalid files(eg. nonconsistent file type between inode node and
dentry nodes, file has no dentry nodes(excepts '/'), encrypted file has
no xattr information, etc.), which will be done in next step.

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>