Fix --enable-qt5

...after b36ea44dcbdb862b0ac6e6cdaf27225b43dc0c7e "push logic from
ImpBitmap::ImplReleaseBuffer down"

Change-Id: I781a79146880686b2396e783da6ed2d1304c7e38
diff --git a/vcl/qt5/Qt5Bitmap.cxx b/vcl/qt5/Qt5Bitmap.cxx
index f5c943d..7ec43af 100644
--- a/vcl/qt5/Qt5Bitmap.cxx
+++ b/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();