lavfi: Move avcodec header to the only filter needing it

af_ashowinfo, due to the enum AVAudioServiceType use.

libavfilter/af_ashowinfo.c

@@ -36,6 +36,8 @@
 #include "libavutil/replaygain.h"
 #include "libavutil/samplefmt.h"
 
+#include "libavcodec/avcodec.h"
+
 #include "audio.h"
 #include "avfilter.h"
 #include "internal.h"

libavfilter/avfilter.h

@@ -40,7 +40,6 @@
 #include "libavutil/samplefmt.h"
 #include "libavutil/pixfmt.h"
 #include "libavutil/rational.h"
-#include "libavcodec/avcodec.h"
 
 #include <stddef.h>