MAINTAINERS: Add qapi/virtio.json to section "virtio"

Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20221020120458.80709-1-armbru@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

MAINTAINERS

@@ -2017,6 +2017,7 @@ S: Supported
 F: hw/*/virtio*
 F: hw/virtio/Makefile.objs
 F: hw/virtio/trace-events
+F: qapi/virtio.json
 F: net/vhost-user.c
 F: include/hw/virtio/