tf-m-build-docs: fix publishing

The bash path expansion used is not available under posix sh,
so don't use it.

Change-Id: I0bbeb0ecbed84597d550344cd3740f55b7695c8c
diff --git a/jenkins/build-docs.jpl b/jenkins/build-docs.jpl
index 80d4a7f..f44d2c4 100644
--- a/jenkins/build-docs.jpl
+++ b/jenkins/build-docs.jpl
@@ -93,7 +93,8 @@
   }
   node("master") {
     sh """
-    cp -a /var/jenkins_home/jobs/tf-m-build-docs/builds/$BUILD_NUMBER/archive/trusted-firmware-m/build/docs/{reference_manual,user_guide} /var/jenkins_home/docs/
+    cp -a /var/jenkins_home/jobs/tf-m-build-docs/builds/$BUILD_NUMBER/archive/trusted-firmware-m/build/docs/reference_manual /var/jenkins_home/docs/
+    cp -a /var/jenkins_home/jobs/tf-m-build-docs/builds/$BUILD_NUMBER/archive/trusted-firmware-m/build/docs/user_guide /var/jenkins_home/docs/
     """
   }
 }