CVE-2026-74329: watchdog: unregister PM notifier on watchdog unregister

In the Linux kernel, the following vulnerability has been resolved:

watchdog: unregister PM notifier on watchdog unregister

watchdogregisterdevice() registers wdd->pmnb when WDOGNOPINGONSUSPEND is set, but watchdogunregisterdevice() does not remove it. This leaves an embedded notifier block on the PM notifier chain after the watchdog device has been unregistered.

A later suspend/resume notification can then call watchdogpmnotifier() with a stale watchdogdevice pointer, or at minimum after wdd->wddata has been cleared by watchdogdevunregister().

Unregister the PM notifier before tearing down the watchdog device.