task_wdt: ensure hw wdt is started before being fed

If a fallback hardware watchdog is used, it is fed together with the
task watchdog in task_wdt_feed. However, the hardware watchdog was
not yet set up before the first call to task_wdt_feed.

This commit fixes the order of wdt_setup and task_wdt_feed calls.

Fixes #39523

Signed-off-by: Martin Jäger <martin@libre.solar>