test: dm: wdt: replace cyclic_run() by schedule()

test: dm: wdt: replace cyclic_run() by schedule()

This is the last place outside of cyclic.c that references
cyclic_run() directly. Replace by schedule(), so that cyclic_run() can
be made private. This also better matches what I believe commit
29caf9305b6f ("cyclic: Use schedule() instead of WATCHDOG_RESET()")
intended to do.

Signed-off-by: Rasmus Villemoes <ravi@prevas.dk>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stefan Roese <sr@denx.de>