Silence an incompatible-pointer-types-discards-qualifiers warning from clang.
rangecoder.c:58:34: warning: passing
      'uint8_t **' (aka 'unsigned char **') to parameter of type
      'const uint8_t **' (aka 'const unsigned char **') discards qualifiers in
      nested pointer types [-Wincompatible-pointer-types-discards-qualifiers]