tf-a-static-checks: Add GERRIT_BRANCH param

This is passed from upstream jobs and needed to reproduce builds.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I9578bf1118e24dbd946594faa3c4455a1f4ac719
diff --git a/tf-a-static-checks.yaml b/tf-a-static-checks.yaml
index 0c23fc9..cf41a6a 100644
--- a/tf-a-static-checks.yaml
+++ b/tf-a-static-checks.yaml
@@ -42,6 +42,9 @@
             description: |-
                 Repository to run static checks on.
         - string:
+            name: GERRIT_BRANCH
+            default: ''
+        - string:
             name: SHARE_FOLDER
             default: '/srv/shared/${JOB_NAME}/${BUILD_NUMBER}'
             description: 'Folder containing shared repositories for downstream pipeline jobs'