qga: fix guest-get-disks regression

Commit 54aa3de7 ("qapi: Use QAPI_LIST_PREPEND() where possible")
inadvertently removed the has_dependencies from the partition disk
info, resulting in empty list being returned.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1950833



Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-id: 20210420125831.233092-1-marcandre.lureau@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>