watchdog: cpu5wdt.c: Fix use-after-free bug caused by cpu5wdt_trigger

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

watchdog: cpu5wdt.c: Fix use-after-free bug caused by cpu5wdt_trigger

When the cpu5wdt module is removing, the origin code uses del_timer() to

de-activate the timer. If the timer handler is running, del_timer() could

not stop it and will return directly. If the port region is released by

release_region() and then the timer handler cpu5wdt_trigger() calls outb()

to write into the region that is released, the use-after-free bug will

happen.

Change del_timer() to timer_shutdown_sync() in order that the timer handler

could be finished before the port region is released.