The watchdog timer value was never updated in the hardware by this
driver, so the watchdog triggered on some random stale value that
was left in the hardware. The TI SPRUH37C says, quote:
20.4.3.9 Modifying Timer Count/Load Values and Prescaler Setting
...
After a write access, the load register value and prescaler ratio
registers are updated immediately, but new values are considered
only after the next consecutive counter overflow or after a new
trigger command (the WDT_WTGR register).
This means at least one trigger must happen. The driver probably
depended on someone calling it's .reset() callback, however that
is not guaranteed e.g. if the WDT operates without servicing.