watchdog: stm32_iwdg: don't print an error on probe deferral

Do not print an error trace when deferring probe for clock resources.

Signed-off-by: Etienne Carriere <etienne.carriere@st.com>
Signed-off-by: Christophe Roullier <christophe.roullier@st.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20201106142327.3129-2-christophe.roullier@st.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>