mc146818rtc: put it into the 'misc' category

The category of the mc146818rtc device is not set, put it into the 'misc'
category.

Signed-off-by: Gan Qixin <ganqixin@huawei.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20201130083630.2520597-6-ganqixin@huawei.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

hw/rtc/mc146818rtc.c

@@ -1039,6 +1039,7 @@ static void rtc_class_initfn(ObjectClass *klass, void *data)
     dc->vmsd = &vmstate_rtc;
     isa->build_aml = rtc_build_aml;
     device_class_set_props(dc, mc146818rtc_properties);
+    set_bit(DEVICE_CATEGORY_MISC, dc->categories);
 }
 
 static const TypeInfo mc146818rtc_info = {