ec_sign_finalize
ATTRIBUTE_WARN_UNUSED_RET int ec_sign_finalize(struct ec_sign_context *ctx, u8 *sig, u8 siglen);
ret = ec_sign_finalize(&ctx, sig, siglen);
ret = ec_sign_finalize(&ctx, sig, siglen);
ret = ec_sign_finalize(&sig_ctx, sig, siglen);