fixing param in voltha-automated-build

Change-Id: I06a95f117aece040fd8124b33a18ce827613d055
diff --git a/jjb/voltha-automated-build.yaml b/jjb/voltha-automated-build.yaml
index 6daa512..3150c13 100644
--- a/jjb/voltha-automated-build.yaml
+++ b/jjb/voltha-automated-build.yaml
@@ -43,7 +43,7 @@
 
       - string:
          name: manifestBranch
-         default: '$GERRIT_BRANCH'
+         default: 'master'
          description: 'Name of the repo branch to use'
 
     project-type: pipeline