Save password requirements on the right user

When changing the password requirements, two changes have to be saved:
(1) Whether the current password complies with the new password
requirements.
(2) The new password requirements themselves.

(1) is stored on the credential owner of the user, (2) is stored on the
user itself.

In ag/3729963 (Change-ID: Ide5b2e53cf100b087822844ca51b3bc69e7ddf82),
we've switched from saving the password sufficiency flag (1) in the
user to the credential owner.
A side effect was that the password requirements themselves, (2), which
were changed on the original user the call related to, were not saved.

This fixes the bug introduced in the aforementioned CL.

Bug: 78499736
Test: Manual with TestDPC.
Change-Id: I11faef37fa6f0e8e8e558069e77021c48ee36cd4