Clear the previous biometric message only after the next face acquisition starts again.

Bug: 340398696
Test: verified manually,
  1. Enroll face auth
  2. Disable camera using privacy toggle
  3. Go to lockscreen
  4. The error message should be displayed only once and should not flash again and again
Flag: NONE bugfix
Change-Id: I8bc5bb2577e896f23634b6857b652394a9a34b51