dt-bindings: timestamp: Correct id path

During the repository renaming from hte to timestamp, $id path was not
updated accordingly. This patch corrects $id path.

Fixes: af583852 ("dt-bindings: Renamed hte directory to timestamp")
Signed-off-by: Dipen Patel <dipenp@nvidia.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>