Comment # 9 on bug 1176454 from Michael Hirmke

(In reply to Oliver Schmidt from comment #8)
> Okay, ignore the last attachment, I just used a wrong zypper syntax.
> 
> Workaround that fixed my system:
> 1. chroot into the system, make sure /boot is mounted as well
> 2. downgrade systemd to last known working version: `zypper in --oldpackage
> --allow-downgrade systemd-234-lp152.31.4.1`
> 3. `mkinitrd`
> 4. reboot
> 
> That fixed it for me, for now I have added a lock on systemd to prevent this
> from happening again as long as the core issue is still here.

Yep, this is exactly my workaround.
During  the first attempt I forgot to run mkinitrd, therefore it failed.
The second time I ran mkinitrd and it worked as expected.