rtpulpfec: fix debug log printf format warning on 32-bit platforms

https://bugzilla.gnome.org/show_bug.cgi?id=793732
diff --git a/gst/rtp/gstrtpulpfecdec.c b/gst/rtp/gstrtpulpfecdec.c
index 28a0a69..eba3436 100644
--- a/gst/rtp/gstrtpulpfecdec.c
+++ b/gst/rtp/gstrtpulpfecdec.c
@@ -414,7 +414,7 @@
     else
       ++self->packets_recovered;
     GST_DEBUG_OBJECT (self, "Unrecovered / Recovered: %lu / %lu",
-        self->packets_unrecovered, self->packets_recovered);
+        (gulong) self->packets_unrecovered, (gulong) self->packets_recovered);
   } else if (GST_EVENT_CAPS == GST_EVENT_TYPE (event)) {
     GstCaps *caps;
     gboolean have_caps_pt = FALSE;