net/sunrpc: Use static const char arrays

context_derive_keys_rc4(struct krb5_ctx *ctx)

{

	struct crypto_hash *hmac;

	char sigkeyconstant[] = "signaturekey";

	static const char sigkeyconstant[] = "signaturekey";

	int slen = strlen(sigkeyconstant) + 1;	/* include null terminator */

	struct hash_desc desc;

	struct scatterlist sg[1];