Pie Controls: Fix sound effects.

After the pie service commits, sound effects were broken for
HOME and BACK keys.

This commit fixes this, by moving the play back of the sound
effect from the injection directly to the onClick().

Change-Id: Id59848ccddac20cef80500f6e72d76afa97ae093

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/policy/PieController.java