avutil/audio_fifo: Use av_fifo_freep() and remove redundant if()

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/audio_fifo.c

@@ -48,8 +48,7 @@ void av_audio_fifo_free(AVAudioFifo *af)
         if (af->buf) {
             int i;
             for (i = 0; i < af->nb_buffers; i++) {
-                if (af->buf[i])
-                    av_fifo_free(af->buf[i]);
+                av_fifo_freep(&af->buf[i]);
             }
             av_freep(&af->buf);
         }