Don't dump commit message header to devstack-version

Dumping commit message to /usr/local/bin/devstack-version
has broken devstack build, because of bash error in formatting.
error log [1].

[1]. http://logs.openstack.org/20/418720/6/check/gate-tempest-dsvm-networking-odl-boron-snapshot-v2driver/ed9fd45/logs/devstacklog.txt.gz

Change-Id: I4c269a7f3d63ee9a976e7c3636fc3e5e8dab9ae3
diff --git a/functions b/functions
index 738040d..f04bc1f 100644
--- a/functions
+++ b/functions
@@ -754,7 +754,7 @@
 function write_devstack_version {
     pushd $TOP_DIR
     local git_version=""
-    git_version=$(git log --format="%H %s %ci" -1)
+    git_version=$(git log --format="%H %ci" -1)
     cat - > /tmp/devstack-version <<EOF
 #!/bin/bash