Fix 'set but not used' ARM compiler warning
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 413dfc2..3915315 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -4151,6 +4151,7 @@
         if( ( ret = mbedtls_ecdh_read_public( &ssl->handshake->ecdh_ctx,
                                       p, end - p) ) != 0 )
         {
+            ((void) ret);
             MBEDTLS_SSL_DEBUG_RET( 1, "mbedtls_ecdh_read_public", ret );
             return( MBEDTLS_ERR_SSL_BAD_HS_CLIENT_KEY_EXCHANGE_RP );
         }