GStreamer: fix compilation with version < 0.10.31.

Qt 5.4 and earlier required GStreamer 0.10.24 as minimum version.
Qt 5.5 added code that requires 0.10.31, this code is now ifdef'd
and we now support again 0.10.24.

Task-number: QTBUG-48353
Change-Id: Ie708a33c0515874b003ce26a3400475075d316ca
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>

src/multimedia/gsttools_headers/qvideosurfacegstsink_p.h

@@ -157,7 +157,12 @@ private:
 
     static gboolean unlock(GstBaseSink *sink);
 
+#if GST_CHECK_VERSION(0, 10, 25)
     static GstFlowReturn show_frame(GstVideoSink *sink, GstBuffer *buffer);
+#else
+    static GstFlowReturn preroll(GstBaseSink *sink, GstBuffer *buffer);
+    static GstFlowReturn render(GstBaseSink *sink, GstBuffer *buffer);
+#endif
 
 private:
     QVideoSurfaceGstDelegate *delegate;