ControllerInterface: Switch to std::shared_ptr

Small cleanup by using std::shared_ptr and getting rid of
ciface.Devices() which just returned the m_devices (which defeats the
point of making m_devices protected).

Incidentally, this should make the code safer when we have
different threads accessing devices in the future (for hotplug?).

A lot of code use Device references directly so there is
no easy way to remove FindDevice() and make those unique_ptrs.

Source/Core/InputCommon/ControllerInterface/Android/Android.cpp

@@ -13,7 +13,7 @@ namespace Android
 void Init()
 {
   for (int i = 0; i < 8; ++i)
-    g_controller_interface.AddDevice(new Touchscreen(i));
+    g_controller_interface.AddDevice(std::make_shared<Touchscreen>(i));
 }
 
 // Touchscreens and stuff