Don't increment the number of channels returned by libdvdnav. This wa…

…s causing 5.1 audio to be wrongly identified as 7 channel, and stereo as 3 channel.

(cherry picked from commit 20a5628)

mythtv/libs/libmythtv/DVDRingBuffer.cpp

@@ -1347,7 +1347,7 @@ uint8_t DVDRingBufferPriv::GetNumAudioChannels(int id)
     unsigned char channels = dvdnav_audio_stream_channels(m_dvdnav, id);
     if (channels == 0xff)
         return 0;
-    return (uint8_t)channels + 1;
+    return (uint8_t)channels;
 }
 
 /** \brief Get the dvd title and serial num