staging: vchi: Get rid of struct vchi_instance_handle

staging: vchi: Get rid of struct vchi_instance_handle

The idea behind this was to create an opaque handle to struct
vchiq_instance. This can be achieved without creating a new type by
means of a forward declaration of struct vchiq_instance.

This saves us from a lot of useless casting and overall simplifies code.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Link: https://lore.kernel.org/r/20200629150945.10720-12-nsaenzjulienne@suse.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>