Add missing ECDH dependency in tls 1.3 client

Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index 2b59b4a..8510d8f 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -379,6 +379,7 @@
                                               const unsigned char *buf,
                                               const unsigned char *end )
 {
+#if defined(MBEDTLS_ECDH_C)
     const mbedtls_ecp_curve_info *curve_info = NULL;
     const unsigned char *p = buf;
     int selected_group;
@@ -435,6 +436,12 @@
     ssl->handshake->offered_group_id = selected_group;
 
     return( 0 );
+#else
+    (void) ssl;
+    (void) buf;
+    (void) end;
+    return( MBEDTLS_ERR_SSL_BAD_CONFIG );
+#endif
 }
 
 /*