vc2enc: set quantization ceiling to 50

The reference encoder limits it to 64, but testing revealed that there
is absolutely no difference for indices above 50 in amount of zeroed
coefficients.
Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>

libavcodec/vc2enc.c

@@ -30,7 +30,7 @@
 #include "diractab.h"
 
 /* Quantizations above this usually zero coefficients and lower the quality */
-#define MAX_QUANT_INDEX 100
+#define MAX_QUANT_INDEX 50
 
 #define COEF_LUT_TAB 2048