Add missing MBEDTLS_ECP_C dependency

Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index ca88b98..09a2df2 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -937,8 +937,12 @@
                                        MBEDTLS_SSL_PRESET_DEFAULT );
     TEST_ASSERT( ret == 0 );
 
+#if defined(MBEDTLS_ECP_C)
     if( curves != NULL )
         mbedtls_ssl_conf_curves( &(ep->conf), curves );
+#else
+    (void) curves;
+#endif
 
     ret = mbedtls_ssl_setup( &( ep->ssl ), &( ep->conf ) );
     TEST_ASSERT( ret == 0 );