uboot-phytec

watchdog: cdns: Add comment for expire_now function

IP itself has no reg/no bit which can be used for this functionality.
Add this note to the driver to make sure that none will be asking for
that. Current method is to setup 1s timeout and hang() which is done via
wdt_expire_now().

Signed-off-by: Michal Simek <michal.simek@xilinx.com>