Low: fencer: Correct refresh logic in update_cib_cache_cb()

We should only be able to call watchdog_device_update() once -- do
either a full refresh or a partial refresh as needed, and then call
watchdog_device_update().

Full vs. partial updates got a bit muddled in 243139b.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>