sandbox: Correct header file order in cpu.c

The dm/ file should go at the end. Move it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/cpu/cpu.c b/arch/sandbox/cpu/cpu.c
index 196f3e1..7a622c8 100644
--- a/arch/sandbox/cpu/cpu.c
+++ b/arch/sandbox/cpu/cpu.c
@@ -4,10 +4,10 @@
  */
 #define DEBUG
 #include <common.h>
-#include <dm/root.h>
 #include <os.h>
 #include <asm/io.h>
 #include <asm/state.h>
+#include <dm/root.h>
 
 DECLARE_GLOBAL_DATA_PTR;