Shave 10us off of hwuitask

This prevents an issue where if the signal schedules
hwuiTask it will immediately block and go back to sleep due
to mLock still being held.

This costs 10us in thread scheduling ping-ponging bouncing
between hwuiTask and RenderThread

Change-Id: I47595c1bf5736576483a6aa7aada0b1be1e04268