Rename forgotten rgb24 and rgb24a after MLT 7 port

src/mltcontroller/clipcontroller.cpp

@@ -223,7 +223,7 @@ void ClipController::getInfoForProducer()
     } else if (m_service == QLatin1String("colour") || m_service == QLatin1String("color")) {
         m_clipType = ClipType::Color;
         // Required for faster compositing
-        m_masterProducer->set("mlt_image_format", "rgb24");
+        m_masterProducer->set("mlt_image_format", "rgb");
         m_hasLimitedDuration = false;
     } else if (m_service == QLatin1String("kdenlivetitle")) {
         if (!m_path.isEmpty()) {

src/timeline2/model/timelinemodel.cpp

@@ -124,7 +124,7 @@ TimelineModel::TimelineModel(Mlt::Profile *profile, std::weak_ptr<DocUndoStack>
     m_blackClip->set("mlt_type", "producer");
     m_blackClip->set("aspect_ratio", 1);
     m_blackClip->set("length", INT_MAX);
-    m_blackClip->set("mlt_image_format", "rgb24a");
+    m_blackClip->set("mlt_image_format", "rgba");
     m_blackClip->set("set.test_audio", 0);
     m_blackClip->set_in_and_out(0, TimelineModel::seekDuration);
     m_tractor->insert_track(*m_blackClip, 0);