Using local variable for token_cache.

Using local variable for token_cache.

The difference with the old code is that originally the whole token_cache
was initialized with zeros at the beginning of decode_coefs() function.
Now we set several zero values explicitly with "token_cache[scan[c]] = 0".

Change-Id: I88cc5031f01d13012d1a4491739c36cb44f9401e