jenkins/: Use tfgit.checkout_ci_scripts()

Consistently use single function for clone tf-m-ci-scripts repo with
parameters defined by job (e.g. specifying a change reference to fetch).

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I76eb4c6c31633b98489f82d29015c7d9486418ff
diff --git a/jenkins/cppcheck.jpl b/jenkins/cppcheck.jpl
index 46e6956..632c60f 100644
--- a/jenkins/cppcheck.jpl
+++ b/jenkins/cppcheck.jpl
@@ -15,7 +15,7 @@
     stage("Init") {
       cleanWs()
       dir("tf-m-ci-scripts") {
-        checkout([$class: 'GitSCM', branches: [[name: '$CI_SCRIPTS_BRANCH']], userRemoteConfigs: [[credentialsId: 'GIT_SSH_KEY', url: '$CI_SCRIPTS_REPO']]])
+        tfgit.checkout_ci_scripts()
         sh "./clone.sh"
       }
     }