staging: vchi: Get rid of struct vchiq_instance forward declaration

It's already forward declared in vchiq_if.h. So no need to insist
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Link: https://lore.kernel.org/r/20200629150945.10720-36-nsaenzjulienne@suse.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vc04_services/interface/vchi/vchi.h

@@ -4,13 +4,6 @@
 #ifndef VCHI_H_
 #define VCHI_H_
 
-/******************************************************************************
- * Global defs
- *****************************************************************************/
-
-// Opaque handle for a VCHIQ instance
-struct vchiq_instance;
-
 /******************************************************************************
  * Global funcs - implementation is specific to which side you are on
  * (local / remote)