dtsdownmix: fix caps negotiation for GStreamer 1.0
dtsdownmix: fix caps negotiation for GStreamer 1.0

 From: Athanasios Oikonomou <athoik@gmail.com>
 Date: Mon, 23 Mar 2015 20:57:06 +0200
 dtsdowmix did not worked on GStreamer 1.0 because caps did not negotiate.
 In order to negotiate caps on GStreamer 1.0 we need to handle missing GST_EVENT_CAPS sink event.

 Changes to be committed:
	modified:   gstdtsdownmix.c

christophecvr/gstreamer1.0-plugin-multibox-dvbmediasink,dazulrich/gstreamer1.0-plugin-multibox-dvbmediasink,vitmod/gstreamer1.0-plugin-multibox-dvbmediasink,sklnet/gstreamer1.0-plugin-multibox-dvbmediasink