avcodec.h: update audioconvert.h header after rename

Found-by: durandal_1707
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/avcodec.h

@@ -30,11 +30,11 @@
 #include "libavutil/samplefmt.h"
 #include "libavutil/avutil.h"
 #include "libavutil/cpu.h"
+#include "libavutil/channel_layout.h"
 #include "libavutil/dict.h"
 #include "libavutil/log.h"
 #include "libavutil/pixfmt.h"
 #include "libavutil/rational.h"
-#include "libavutil/audioconvert.h"
 
 #include "libavcodec/version.h"
 /**