jobs/master-builds: use osmo-iuh/master for asn1c

As discussed with Pau, let's build the "osmo-iuh/master" branch of our
asn1c.git repository in jenkins. This branch is what we actually use for
osmo-iuh and "master" should track upstream master.

Related: OS#2435
Change-Id: Ic97a23a175b301e6f42f7ca67deb84dcc3ee3f90

jobs/master-builds.yml

@@ -48,12 +48,16 @@
     trigger:
     email: jenkins-notifications@lists.osmocom.org laforge@gnumonks.org
     git_base_url: https://gerrit.osmocom.org
+    branches:
+      - master
     ssh:
       - docs_ftp.osmocom.org
 
     # in alphabetical order
     repos:
-      - asn1c
+      - asn1c:
+          branches:
+            - osmo-iuh/master
 
       - libasn1c:
           # Full triggers would be:
@@ -518,8 +522,7 @@
     scm:
       - git:
          url: "{git_base_url}/{repos}"
-         branches:
-           - 'origin/master'
+         branches: '{obj:branches}'
          refspec:
          name:
          wipe-workspace: false