v4l2videodec: return right type for drain.

https://bugzilla.gnome.org/show_bug.cgi?id=752962

UpStream Status: Pending
diff --git a/sys/v4l2/gstv4l2videodec.c b/sys/v4l2/gstv4l2videodec.c
index 8fd3ccc..0d657da 100644
--- a/sys/v4l2/gstv4l2videodec.c
+++ b/sys/v4l2/gstv4l2videodec.c
@@ -428,7 +428,7 @@
   return ret;
 }
 
-static gboolean
+static GstFlowReturn
 gst_v4l2_video_dec_drain (GstVideoDecoder * decoder)
 {
   GstV4l2VideoDec *self = GST_V4L2_VIDEO_DEC (decoder);
@@ -437,7 +437,7 @@
   gst_v4l2_video_dec_finish (decoder);
   gst_v4l2_video_dec_flush (decoder);
 
-  return TRUE;
+  return GST_FLOW_OK;
 }
 
 static GstVideoCodecFrame *