avcodec: disable FF_API_FAST_MALLOC

It causes build failures in some cases and the functions are provided by
libavutil so the wraper should not be needed anymore

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

libavcodec/version.h

@@ -133,7 +133,7 @@
 #define FF_API_MAX_BFRAMES       (LIBAVCODEC_VERSION_MAJOR < 57)
 #endif
 #ifndef FF_API_FAST_MALLOC
-#define FF_API_FAST_MALLOC       (LIBAVCODEC_VERSION_MAJOR < 57)
+#define FF_API_FAST_MALLOC       (LIBAVCODEC_VERSION_MAJOR < 56)
 #endif
 #ifndef FF_API_NEG_LINESIZES
 #define FF_API_NEG_LINESIZES     (LIBAVCODEC_VERSION_MAJOR < 57)