ui/vc: change the argument for QemuTextConsole

Those functions are specifc to text/vc console, make that explicit from
the argument type.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230830093843.3531473-45-marcandre.lureau@redhat.com>