moxie: Fix warning caused by missing include statement

Warning from the Sparse static analysis tool:

target-moxie/machine.c:4:26:
 warning: symbol 'vmstate_moxie_cpu' was not declared. Should it be static?

machine.h includes the missing declaration.

Cc: Anthony Green <green@moxielogic.com>
Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

target-moxie/machine.c

diff --git a/target-moxie/machine.c b/target-moxie/machine.c
index da1a857..b9316f0 100644
--- a/target-moxie/machine.c
+++ b/target-moxie/machine.c
@@ -1,5 +1,6 @@
 #include "hw/hw.h"
 #include "hw/boards.h"
+#include "machine.h"
 
 const VMStateDescription vmstate_moxie_cpu = {
     .name = "cpu",