Remus: fix a warning

This patch fixes the following warning:
  xen/lowlevel/checkpoint/libcheckpoint.c: In function
  `delete_suspend_timer':
  xen/lowlevel/checkpoint/libcheckpoint.c:352: warning: assignment
  makes integer from pointer without a cast

Signed-off-by: KUWAMURA Shin'ya <kuwa@jp.fujitsu.com>

tools/python/xen/lowlevel/checkpoint/libcheckpoint.c

@@ -349,7 +349,7 @@ int delete_suspend_timer(checkpoint_state* s)
   if (s->timer) {
     if ((rc = timer_delete(s->timer)))
       fprintf(stderr, "Error deleting timer: %s\n", strerror(errno));
-    s->timer = NULL;
+    s->timer = 0;
   }
 
   return rc;