ext/dts/gstdtsdec.c: Fix flow handling and buffer refcounting (gst_pad_push() takes ownership of the buffer passed to...

Original commit message from CVS:
* ext/dts/gstdtsdec.c: (gst_dtsdec_handle_frame):
Fix flow handling and buffer refcounting (gst_pad_push() takes
ownership of the buffer passed to it, the buffer does not have
to be unreffed no matter what flow value gst_pad_push() returns).