hw/s390x: Clean up global variable shadowing in quiesce_powerdown_req()

Fix:

  hw/s390x/sclpquiesce.c:90:22: error: declaration shadows a variable in the global scope [-Werror,-Wshadow]
      QuiesceNotifier *qn = container_of(n, QuiesceNotifier, notifier);
                       ^
  hw/s390x/sclpquiesce.c:86:3: note: previous declaration is here
  } qn;
    ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-Id: <20231010115048.11856-7-philmd@linaro.org>

hw/s390x/sclpquiesce.c

@@ -78,12 +78,10 @@ static const VMStateDescription vmstate_sclpquiesce = {
      }
 };
 
-typedef struct QuiesceNotifier QuiesceNotifier;
-
-static struct QuiesceNotifier {
+typedef struct QuiesceNotifier {
     Notifier notifier;
     SCLPEvent *event;
-} qn;
+} QuiesceNotifier;
 
 static void quiesce_powerdown_req(Notifier *n, void *opaque)
 {
@@ -97,6 +95,8 @@ static void quiesce_powerdown_req(Notifier *n, void *opaque)
 
 static int quiesce_init(SCLPEvent *event)
 {
+    static QuiesceNotifier qn;
+
     qn.notifier.notify = quiesce_powerdown_req;
     qn.event = event;