qdev: change first argument of qbus_create_inplace to void *

Make it clear that no BUS() macro is needed in the callers (in fact it
wouldn't work because the object has not been initialized yet with the
right class).

Suggested-by: Andreas Faerber <afaerber@suse.de>
Acked-by: Andreas F=E4rber <afaerber@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
