hwmon: (ds1621) Use kobj_to_dev()

fixed the following coccicheck:
./drivers/hwmon/ds1621.c:329:60-61: WARNING opportunity
for kobj_to_dev().

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Link: https://lore.kernel.org/r/1616032504-59817-1-git-send-email-tiantao6@hisilicon.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>