stm32f2xx_timer: delay timer_new to avoid memleaks

There is a memory leak when we call 'device_list_properties' with typename = stm32f2xx_timer. It's easy to reproduce as follow:

    virsh qemu-monitor-command vm1 --pretty '{"execute": "device-list-properties", "arguments": {"typename": "stm32f2xx_timer"}}'

This patch delay timer_new to fix this memleaks.

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Pan Nengyuan <pannengyuan@huawei.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20200205070659.22488-3-pannengyuan@huawei.com
Cc: Alistair Francis <alistair@alistair23.me>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/timer/stm32f2xx_timer.c

@@ -314,7 +314,11 @@ static void stm32f2xx_timer_init(Object *obj)
     memory_region_init_io(&s->iomem, obj, &stm32f2xx_timer_ops, s,
                           "stm32f2xx_timer", 0x400);
     sysbus_init_mmio(SYS_BUS_DEVICE(obj), &s->iomem);
+}
 
+static void stm32f2xx_timer_realize(DeviceState *dev, Error **errp)
+{
+    STM32F2XXTimerState *s = STM32F2XXTIMER(dev);
     s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, stm32f2xx_timer_interrupt, s);
 }
 
@@ -325,6 +329,7 @@ static void stm32f2xx_timer_class_init(ObjectClass *klass, void *data)
     dc->reset = stm32f2xx_timer_reset;
     device_class_set_props(dc, stm32f2xx_timer_properties);
     dc->vmsd = &vmstate_stm32f2xx_timer;
+    dc->realize = stm32f2xx_timer_realize;
 }
 
 static const TypeInfo stm32f2xx_timer_info = {