Fix warnings about unused variables.

Change-Id: I147ff8624faa98396d6c48801c41a731fd02ac10
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>

src/plugins/directshow/camera/dscamerasession.cpp

@@ -96,6 +96,8 @@ public:
 
     STDMETHODIMP SampleCB(double Time, IMediaSample *pSample)
     {
+        Q_UNUSED(Time)
+        Q_UNUSED(pSample)
         return E_NOTIMPL;
     }