InputCommon: Use nested namespace specifiers where applicable

Source/Core/InputCommon/ControllerInterface/DInput/DInput.cpp

@@ -14,9 +14,7 @@
 #pragma comment(lib, "Dinput8.lib")
 #pragma comment(lib, "dxguid.lib")
 
-namespace ciface
-{
-namespace DInput
+namespace ciface::DInput
 {
 BOOL CALLBACK DIEnumDeviceObjectsCallback(LPCDIDEVICEOBJECTINSTANCE lpddoi, LPVOID pvRef)
 {
@@ -69,5 +67,4 @@ void PopulateDevices(HWND hwnd)
 
   idi8->Release();
 }
-}  // namespace DInput
-}  // namespace ciface
+}  // namespace ciface::DInput