Fix off by one in an assert.

'bits' can be (less than or) equal to sizeof(av1_cat6_prob).

BUG=aomedia:399

Change-Id: I20ceb6fa3b61dfcc59e28605fe4f90d8bfaacc51

av1/common/entropy.h

@@ -120,7 +120,7 @@ static INLINE int av1_get_cat6_extrabits_size(TX_SIZE tx_size,
   if (tx_size > TX_32X32) tx_size = TX_32X32;
 #endif
   int bits = (int)bit_depth + 3 + (int)tx_size;
-  assert(bits < (int)sizeof(av1_cat6_prob));
+  assert(bits <= (int)sizeof(av1_cat6_prob));
   return bits;
 }