watchdog: dw_wdt: Fix duplicate included linux/kernel.h

Clean up the following includecheck warning:

./drivers/watchdog/dw_wdt.c: linux/kernel.h is included more than once.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/1620904182-74107-1-git-send-email-jiapeng.chong@linux.alibaba.com


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