Fix clearing of retained password

HW accelerated FDE requires both old and new password to be sent to
secure side to verify and update password. This requires storing of
old password until password is verified. Initial approach of clearing
old password after 60 seconds has a bug which resets old password to
default if user delays entering new password. This fix would gives
caller the responsibility to clear the password once password is
updated.

Change-Id: I0ea5cb92ec3908e31c081ce2af6a190c67aadc7b