staging: vc04_services: Make vchi_msg_queue static

The vchi_msg_queue function which is used by other drivers
to queue a message is difficult to understand and overly
generic.

Make the function static and remove it from the exported
symbols.

Signed-off-by: Michael Zoran <mzoran@crowfest.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>