Fix minor bug that prevents greater's from locking partitions
Looks like a bug was introduced while refactoring the code at some point. This one-liner fixes that.
No material impact since the greeter doesn’t currently implement locking but worth fixing so that future lock-implementers aren’t left with a nasty surprise.
Feature Branch: tails:feature/15653-15656-greeter-unlock,greeter:feature/15653-15656-greeter-unlock