platform/chrome: cros_ec: Fix panic notifier registration

platform/chrome: cros_ec: Fix panic notifier registration

Initialize panic notifier to avoid the following lockdep warning:

INFO: trying to register non-static key.
The code is fine but needs lockdep annotation, or maybe
you didn't initialize this object before use?
turning off the locking correctness validator.
[...]
Hardware name: Samsung Exynos (Flattened Device Tree)
Workqueue: events_unbound async_run_entry_fn
 unwind_backtrace from show_stack
[...]
 blocking_notifier_chain_register from cros_ec_debugfs_probe
 cros_ec_debugfs_probe from platform_probe

Fixes: d90fa2c64d59 ("platform/chrome: cros_ec: Poll EC log on EC panic")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
[tzungbi: trimmed the stack trace in commit message.]
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20230110221033.7441-1-m.szyprowski@samsung.com