mc146818rtc: always register rtc to rtc list

We are not required anymore to use rtc_init() function.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
Message-Id: <20171216090228.28505-5-hpoussin@reactos.org>
[PMD: rebased, fix OBJECT() value]
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20191018133547.10936-5-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>