Make function get_channel_name() static: It is only used in audioconvert.c.

Originally committed as revision 22114 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/audioconvert.c

@@ -79,7 +79,7 @@ static const char* const channel_names[]={
     [30] = "DR",
 };
 
-const char *get_channel_name(int channel_id)
+static const char *get_channel_name(int channel_id)
 {
     if (channel_id<0 || channel_id>=FF_ARRAY_ELEMS(channel_names))
         return NULL;