watchdog: ensure configured timeout is used instead of USEC_INFINITY

watchdog: ensure configured timeout is used instead of USEC_INFINITY

In some rare cases, a watchdog driver might neither be able to change
the watchdog timeout value, nor read it from the hardware at runtime.

With an otherwise functional watchdog setup, this constellation worked
until systemd v249. Since then, systemd ends up ignoring the timeout
defined by the system.conf and rather uses USEC_INFINITY. Consequently,
the watchdog is not pinged anymore and eventually resets the system.

We therefore want to ensure that the system keeps running with the
originally configured timeout.