tf-gerrit-tforg-l2: fix gerrit trigger structure

The review of this job failed the automated sanity check at:

https://review.trustedfirmware.org/c/ci/tf-a-job-configs/+/6384

Fix the trigger to match the documented structure of gerrit triggers at:

https://docs.openstack.org/infra/jenkins-job-builder/triggers.html?highlight=gerrit#triggers.gerrit

So the job can actually be deployed on the server.

Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
Change-Id: I501126caacb40ee1b8c35eb20dbd538551c733dd
1 file changed