MIP405T: fix compile problem

The "stdio/device: rework function naming convention" patch
(commit 52cb4d4f) broke the MIP405T board; this patch fixes it.
Signed-off-by: NWolfgang Denk <wd@denx.de>

board/mpl/common/common_util.c

@@ -429,7 +429,7 @@ void check_env(void)
 }
 
 
-extern device_t *stdio_devices[];
+extern struct stdio_dev *stdio_devices[];
 extern char *stdio_names[];
 
 void show_stdio_dev(void)