MAINTAINERS: Add the staging vchiq driver as a bcm2835 responsibility.

It's being merged to support firmware communication on the Raspberry
Pi, so we should probably send its patches to linux-rpi-kernel.

Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>