QuickSettingsController.java: remove unneeded casts

mContainerView is final and always an instance of QuickSettingsContainerView,
as provided to the constructor. There is no need to hold a reference to a
super-class of it.

Change-Id: Iddca83bf9d251553d4ae9c2d2c54446336f16f6f

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/phone/QuickSettingsController.java