fix 90-systemd-swap.conf so the comment will not be treated as params by modprobe

This doesn't cause an error, but should be fixed so we don't get annoying logs like these:

```
[    4.398682] zram: unknown parameter '#32' ignored
[    4.398685] zram: unknown parameter 'is' ignored
[    4.398686] zram: unknown parameter 'max' ignored
[    4.398687] zram: unknown parameter 'zram' ignored
[    4.398688] zram: unknown parameter 'devices' ignored
[    4.401308] zram: Created 32 device(s) ...
```

This problem was reported downstream at Arch: https://bugs.archlinux.org/task/41354