Without this change, configurations like
```nix
fileSystems."/path/to/bindMountedDirectory" = {
device = "/path/to/originalDirectory";
options = [ "bind" ];
};
```
will lead to a warning message in `dmesg`:
```
systemd-fstab-generator: Checking was requested for "/path/to/originalDirectory", but it is not a device.
```
This happens because the generated /etc/fstab entry contains a non-zero fsck pass number, which doesn't make sense for a bind mount.
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