gpu: host1x: Initialize firewall class to the job's one

The commands stream is prepended by the jobs class on the CDMA
submission, so that explicitly setting a module class in the commands
stream isn't necessary. The firewall initializes its class to 0 and the
command stream that doesn't explicitly specify the class effectively
bypasses the firewall.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Mikko Perttunen <mperttunen@nvidia.com>
Reviewed-by: Erik Faye-Lund <kusmabite@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>