obj-evax.c tidy

obj-evax.c tidy

This started out as fixing decode_16, which used a char to index a 256
byte decodings array.  When char is signed that could result in an out
of bounds array access.  The rest of the patch is for consistency and
just general cleanup.

	* config/obj-evax.c (crc32, encode_32, encode_16, decode_16):
	Remove unnecessary prototypes.
	(number_of_codings): Delete, use ARRAY_SIZE instead throughout.
	(codings, decodings): Make arrays of unsigned char.
	(crc32): Use unsigned variables.  Delete unnecessary mask.
	(encode_32, encode_16): Return unsigned char*, and make static
	buffer an unsigned char array.
	(decode_16): Make arg an unsigned char*.  Remove useless casts.
	(shorten_identifier): Use unsigned char crc_chars.
	(is_truncated_identifier): Make ptr an unsigned char*.