ide: qdev: register ide bus unrealize function

we have an idebus unrealize function, but it was being
registered as the unrealize function for the IDE Device,
so it was not getting invoked on device teardown because
nothing is "unrealizing" the IDE devices themselves.

Suggested-by: John Snow <jsnow@redhat.com>
Signed-off-by: Li Qiang <liqiang6-s@360.cn>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 1488449293-80280-2-git-send-email-liqiang6-s@360.cn
Signed-off-by: John Snow <jsnow@redhat.com>