The OST prescaler bugfix (7a5130a277) broke runtime switching
between 1.0V and 2.0V modes. The 1ms delay after shutting down
the DAC isn't long enough to reset it, so it gets stuck in the
power mode assigned at boot. Change the delay back to 4ms, the
effective value prior to the OST bugfix.
Change-Id: Ic4583d1a6fa82540062aa185386f14bbf785a3f4