Use correct user ID for face bypass pref controller

Ensures that the lockscreen bypass preference toggle shown on the face
unlock settings screen always uses the correct user ID. This fixes an
issue where the preference toggle for a guest user would use the
primary user's setting when multiple biometrics are supported.

Test: Manual:
1. Turn on Settings > System > Multiple users > Use multiple users
2. Add a guest account and switch to it
3. Enroll a face for Face Unlock on the guest account
4. From the Face Unlock settings screen, toggle "Skip lock screen"
5. Ensure that face bypasses lock screen iff this toggle is on
6. Switch back to the owner account and repeat steps 3-5

Fixes: 193488905
Change-Id: I2da4ce466fe0446cccc9119c90bd322daf627339