hwmon: Add missing inclusions of <linux/err.h>

These drivers use IS_ERR so they should include <linux/err.h>.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Luca Tettamanti <kronos.it@gmail.com>
Cc: Henrik Rydberg <rydberg@euromail.se>