ac3dec_fixed: add missing "static const".

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavcodec/ac3dec_fixed.c

@@ -65,7 +65,7 @@ static const uint8_t center_levels[4] = { 4, 5, 6, 5 };
  */
 static const uint8_t surround_levels[4] = { 4, 6, 7, 6 };
 
-int end_freq_inv_tab[8] =
+static const int end_freq_inv_tab[8] =
 {
     50529027, 44278013, 39403370, 32292987, 27356480, 23729101, 20951060, 18755316
 };