Fix compiler warning from unused private field in QSequentialIterable

Change-Id: I9c330b4f99f77404eacda2506d264f917f9e1161
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/corelib/kernel/qiterable.h

@@ -92,6 +92,7 @@ public:
       : m_iterable(p)
       , m_metaSequence(QMetaSequence::fromContainer<T>())
     {
+        Q_UNUSED(m_revision);
     }
 
     QSequentialIterable() = default;