staging: vc04_services: Replace "firmware" node with a compatible lookup.

This was requested by Rob Herring in DT bindings review.

Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>