tf-a-lts2.8-tftf-gerrit-tforg-l*: Set TF_GERRIT_REFSPEC to lts-v2.8 branch

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I9562e0c9c8e758dcb20de3977b178440a958add6
diff --git a/tf-a-lts2.8-tftf-gerrit-tforg-l2.yaml b/tf-a-lts2.8-tftf-gerrit-tforg-l2.yaml
index 80f05c9..ebf32a2 100644
--- a/tf-a-lts2.8-tftf-gerrit-tforg-l2.yaml
+++ b/tf-a-lts2.8-tftf-gerrit-tforg-l2.yaml
@@ -33,6 +33,9 @@
             name: GERRIT_CHANGE_NUMBER
             default: ''
         - string:
+            name: TF_GERRIT_REFSPEC
+            default: '+refs/heads/lts-v2.8:refs/remotes/origin/lts-v2.8'
+        - string:
             name: TFTF_GERRIT_REFSPEC
             default: ${GERRIT_REFSPEC}
             description: 'Parameter only used by the clone script'