Use c3po master branch in post merge jobs

Change-Id: I07e08e2a7aa575823ab7c0f0066a4bde727785d2
diff --git a/jjb/omec-ci.yaml b/jjb/omec-ci.yaml
index 002b00a..ddba9a2 100644
--- a/jjb/omec-ci.yaml
+++ b/jjb/omec-ci.yaml
@@ -19,7 +19,7 @@
       - 'omec-postmerge':
           project: '{name}'
           build-node: 'omec-qa'
-          c3po-branch-name: 'multiUpfs'
+          c3po-branch-name: 'master'
           ngic-branch-name: 'central-cp-multi-upfs'
           openmme-branch-name: 'master'
           pipeline-file: 'omec-postmerge.groovy'