platform/chrome: cros_ec_ishtp: Fix UAF after unbinding driver

platform/chrome: cros_ec_ishtp: Fix UAF after unbinding driver

After unbinding the driver, another kthread `cros_ec_console_log_work`
is still accessing the device, resulting an UAF and crash.

The driver doesn't unregister the EC device in .remove() which should
shutdown sub-devices synchronously.  Fix it.

Fixes: 26a14267aff2 ("platform/chrome: Add ChromeOS EC ISHTP driver")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20251031033900.3577394-1-tzungbi@kernel.org
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>