Fix the text under the "Setup for limited vision or head motion"

is grayed out

Align the sub-title text color with main-title.

Flag: NONE

Bug: 336678451

Test: manually test with reproducible steps then check it visually:
1. Go to Settings > Security & privacy > Device unlock
> Fingerprint & Face Unlock > Face Unlock
2. Confirm your PIN/Pattern/Password
3. Tap on "Setup for limited vision or head motion"

Change-Id: Id6db60d1fc97833607e184bc2fa71b76f46983a4