Fix the listing of `initfs:` directories

There was a bug at the `initfs` generation which made the listing of the contents of the `initfs:`subdirectories impossible from the command line.

The subdirectory listing data had the full paths of the files (like `bin/ahcid\nbin/bgad\n...`) when it should just only be the names of the files (`ahcid\nbgad\n...`)