[CI] Don't run clang-format lint on vendor code

Vendor code doesn't necessarily follow our C/C++ style guide and
shouldn't be checked with clang-format.
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 22b10b5..efaa85b 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -53,7 +53,7 @@
         # get reported to GitHub Checks annotations. Upstream bug report:
         # https://developercommunity.visualstudio.com/content/problem/689794/pipelines-logging-command-logissue-does-not-report.html
         #echo "##vso[task.issue type=error;sourcepath=/azure-pipelines.yml;linenumber=45;columnnumber=1;code=100;]Found something that could be a problem."
-        git diff -U0 $(git merge-base --fork-point origin/master) | clang-format-diff -p1 | tee clang-format-output
+        git diff -U0 $(git merge-base --fork-point origin/master) ':(exclude)hw/vendor' ':(exclude)sw/vendor' | clang-format-diff -p1 | tee clang-format-output
         if [ -s clang-format-output ]; then
           echo -n "##vso[task.logissue type=error]"
           echo "C/C++ lint failed. Use 'util/run-clang-format.sh' or 'git clang-format' to format the code."