watchdog: add error messages when initializing timeout fails

This not only removes boilerplate code from watchdog drivers, it can
also be more specific which of the supplied value actually fails. Also,
the loglevel becomes now consistent across drivers.

Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>