Move wakelock release to handleMessage

There were certain code paths in handleDockStateChange() that were
exiting without releasing the wakelock. So we move the release to the
calling function to prevent stray held wakelocks.

Bug: 16841895

Change-Id: I8ae4d2ab8f775c42a893d3bcdef34321c5f631a6
Signed-off-by: Prashant Malani <pmalani@google.com>