Fix incorrect return code

Code return differs from raw agreement, so tests fail.

Signed-off-by: Paul Elliott <paul.elliott@arm.com>

tf-psa-crypto/core/psa_crypto.c

@@ -7737,7 +7737,7 @@ static psa_status_t validate_key_agreement_params(const psa_key_attributes_t *at
     psa_key_type_t key_type;
 
     if (!PSA_ALG_IS_RAW_KEY_AGREEMENT(alg)) {
-        return PSA_ERROR_INVALID_ARGUMENT;
+        return PSA_ERROR_NOT_SUPPORTED;
     }
 
     key_type = psa_get_key_type(attributes);