watchdog: diag288_wdt: Remove redundant assignment

The assign for 'ret' is redundant and can be removed,
because it will be assigned before use.

Signed-off-by: Junlin Yang <yangjunlin@yulong.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20210203122404.752-1-angkery@163.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>