touch_updater: Add log message for test case parsing

By our customer's request, some log messages with specific pattern
should be added to /var/log/messages for test case parsing.
This patch adds log message with pattern "Product ID: <Product ID>".

Note: This patch might be duplicating another effort.

BUG=b:416642463
TEST=on nissa device with elan touchscreen, version check works.
After script finished, the specific log message can be found in
/var/log/messages.

Change-Id: Iee2ae59cbec89e1d466218b20501f9acbdf0c86d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/touch_updater/+/6539769
Reviewed-by: Henry Barnor <hbarnor@chromium.org>
Reviewed-by: Kenneth Albanowski <kenalba@google.com>
Tested-by: Paul Liang <paul.liang@emc.com.tw>
Reviewed-by: Paul Liang <paul.liang@emc.com.tw>
Commit-Queue: Paul Liang <paul.liang@emc.com.tw>
diff --git a/scripts/chromeos-elan-hid-touch-firmware-update-legacy.sh b/scripts/chromeos-elan-hid-touch-firmware-update-legacy.sh
index b651cbb..8e132e6 100755
--- a/scripts/chromeos-elan-hid-touch-firmware-update-legacy.sh
+++ b/scripts/chromeos-elan-hid-touch-firmware-update-legacy.sh
@@ -275,6 +275,9 @@
     die "No valid firmware for Elan i2chid ${active_product_id} found."
   fi
 
+  # Log "Product ID: <Product ID>" to /var/log/messages for test case parsing
+  log_msg "Product ID: ${active_product_id}"
+
   # Parse out the file name and firmware version from the fw_path.
   fw_version="$(get_fw_version_from_filename "${fw_path}")"
   log_msg "FW version of file: ${fw_version}"