Fix post-merge jobs to use head of merge, not patchset refspec

Change-Id: Ic614f26d55b3f6bf1662546e7b730236932749fe
diff --git a/jjb/sonar.yaml b/jjb/sonar.yaml
index 8173268..97d241c 100644
--- a/jjb/sonar.yaml
+++ b/jjb/sonar.yaml
@@ -101,7 +101,7 @@
     scm:
       - lf-infra-gerrit-scm:
           git-url: '$GIT_URL/$GERRIT_PROJECT'
-          refspec: '$GERRIT_REFSPEC'
+          refspec: 'refs/heads/$GERRIT_BRANCH'
           branch: '$GERRIT_BRANCH'
           submodule-recursive: 'false'
           choosing-strategy: gerrit