hack/update-codegen.sh: fix symlink paths

Wow fun times with symlinks. We *think* this script should work in CI
now...but we'll see.

Previously we were seeing a false positive where even though the generated
code was out of date, the CI step did not report failure.

Signed-off-by: Andrew Keesler <akeesler@vmware.com>

hack/update-codegen.sh

@@ -14,9 +14,10 @@ function codegen() {
     if [[ ${IN_DOCKER:-0} -eq 1 ]]; then
         # Already in a container ($CODEGEN_IMAGE).
         mkdir -p "$(dirname /go/src/$BASE_PKG/$PKG)"
-        ln -sf "$ROOT" "/go/src/$BASE_PKG/$PKG"
+        test -e "/go/src/$BASE_PKG/$PKG" || ln -s "$ROOT" "/go/src/$BASE_PKG/$PKG"
         cd "/go/src/$BASE_PKG/$PKG"
-        /codegen/entrypoint.sh "$@" 2>&1 | sed "s|^|$1 ($PKG) > |"
+        /codegen/entrypoint.sh "$@" 2>&1 \
+          | sed "s|^|$1 ($PKG) > |"
     else
         # Local workstation.
         docker run \