Fix --enable-qt5

...after b36ea44d "push logic from
ImpBitmap::ImplReleaseBuffer down"

Change-Id: I781a79146880686b2396e783da6ed2d1304c7e38

vcl/qt5/Qt5Bitmap.cxx

@@ -215,7 +215,7 @@ BitmapBuffer* Qt5Bitmap::AcquireBuffer(BitmapAccessMode /*nMode*/)
     return pBuffer;
 }
 
-void Qt5Bitmap::ReleaseBuffer(BitmapBuffer* pBuffer, BitmapAccessMode /*nMode*/)
+void Qt5Bitmap::ReleaseBuffer(BitmapBuffer* pBuffer, BitmapAccessMode nMode)
 {
     m_aPalette = pBuffer->maPalette;
     auto count = m_aPalette.GetEntryCount();