Remove return statements following infinite loops without break

These statements cannot be reached and are thus not needed.
This removes a number of compiler warnings.

Signed-off-by: Mans Rullgard <mans@mansr.com>

libavformat/swfdec.c

@@ -204,7 +204,6 @@ static int swf_read_packet(AVFormatContext *s, AVPacket *pkt)
     skip:
         avio_skip(pb, len);
     }
-    return 0;
 }
 
 AVInputFormat ff_swf_demuxer = {