venice: Include env.h to permit reading the environment

This file reads from the environment but does not include the correct
header. Update it.

Signed-off-by: Simon Glass <sjg@chromium.org>

board/gateworks/venice/venice.c

@@ -3,6 +3,7 @@
  * Copyright 2021 Gateworks Corporation
  */
 
+#include <env.h>
 #include <fdt_support.h>
 #include <init.h>
 #include <led.h>