Fix Win32 warning
diff --git a/vl.c b/vl.c
index e4d2887..a210b6c 100644
--- a/vl.c
+++ b/vl.c
@@ -934,7 +934,7 @@
 struct qemu_alarm_win32 {
     MMRESULT timerId;
     unsigned int period;
-} alarm_win32_data = {0, NULL, -1};
+} alarm_win32_data = {0, -1};
 
 static int win32_start_timer(struct qemu_alarm_timer *t);
 static void win32_stop_timer(struct qemu_alarm_timer *t);