Make AVCodec long_names definition conditional depending on CONFIG_SMALL.

Originally committed as revision 13759 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/cook.c

@@ -1195,5 +1195,5 @@ AVCodec cook_decoder =
     .init = cook_decode_init,
     .close = cook_decode_close,
     .decode = cook_decode_frame,
-    .long_name = "COOK",
+    .long_name = NULL_IF_CONFIG_SMALL("COOK"),
 };