chore(coverity): download Coverity Build tool from TF-A OpenCI

By default, the 'run_coverity_on_tf.py' script downloads Coverity Build
tool from 'files.oss.arm.com', which is an internal server only
accessible from within Arm network.

Redirect the script to download the tool from TF-A OpenCI shared folder
instead, which mimics what the 'tf-coverity' job does [1].

[1] https://git.trustedfirmware.org/ci/tf-a-job-configs.git/tree/tf-a-coverity.yaml?id=6349852b8b890c990d68bac846369ce30f3b9a51#n62

Change-Id: I62bdf041523d8dddc4a28432824eca3446e78218
1 file changed