Fix unused function warning

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index 4f5ee97..3831d4a 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -1205,7 +1205,8 @@
 #define SSL_CID_LEN_MIN MBEDTLS_SSL_CID_OUT_LEN_MAX
 #endif
 
-#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
+#if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
+    defined(MBEDTLS_CIPHER_MODE_CBC) && defined(MBEDTLS_AES_C)
 static int psa_cipher_encrypt_helper( mbedtls_ssl_transform *transform,
                     const unsigned char *iv, size_t iv_len,
                     const unsigned char *input, size_t ilen,
@@ -1246,7 +1247,7 @@
                             iv, iv_len, input, ilen, output, olen );
 #endif /* MBEDTLS_USE_PSA_CRYPTO */
 }
-#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
+#endif /* MBEDTLS_SSL_PROTO_TLS1_2 && MBEDTLS_CIPHER_MODE_CBC && MBEDTLS_AES_C */
 
 static int build_transforms( mbedtls_ssl_transform *t_in,
                              mbedtls_ssl_transform *t_out,