staging: mmal-vchiq: Fix memory leak for vchiq_instance

The vchiq_instance is allocated with vchiq_initialise() but never
freed properly. Fix memory leak for the vchiq_instance.

Reported-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Link: https://lore.kernel.org/r/1603706150-10806-1-git-send-email-sw0312.kim@samsung.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>