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
diff --git a/script/tf-coverity/run_coverity_on_tf.py b/script/tf-coverity/run_coverity_on_tf.py
index 39fe9b0..e3c2951 100755
--- a/script/tf-coverity/run_coverity_on_tf.py
+++ b/script/tf-coverity/run_coverity_on_tf.py
@@ -36,8 +36,8 @@
 
 
 def get_coverity_tool():
-    coverity_tarball = "cov-analysis-linux64-2022.06.tar.gz"
-    url = "http://files.oss.arm.com/downloads/tf-a/" + coverity_tarball
+    coverity_tarball = "coverity_tool.tgz"
+    url = "https://downloads.trustedfirmware.org/tf-a/tf-a-coverity/" + coverity_tarball
     print("Downloading Coverity Build tool from %s..." % url)
     file_handle = urllib.request.urlopen(url)
     output = open(coverity_tarball, "wb")