use MAX_BLOCKS for array size instead of 6

Originally committed as revision 14515 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ac3dec.h

@@ -91,7 +91,7 @@ typedef struct {
 
 ///@defgroup aht adaptive hybrid transform
     int channel_uses_aht[AC3_MAX_CHANNELS];                 ///< channel AHT in use     (chahtinu)
-    int pre_mantissa[AC3_MAX_CHANNELS][AC3_MAX_COEFS][6];   ///< pre-IDCT mantissas
+    int pre_mantissa[AC3_MAX_CHANNELS][AC3_MAX_COEFS][MAX_BLOCKS];  ///< pre-IDCT mantissas
 ///@}
 
 ///@defgroup channel channel