hwmon: (i5k_amb) fix checkpatch issues

fixed:
WARNING: simple_strtoul is obsolete, use kstrtoul instead
+	unsigned long temp = simple_strtoul(buf, NULL, 10) / 500;

WARNING: simple_strtoul is obsolete, use kstrtoul instead
+	unsigned long temp = simple_strtoul(buf, NULL, 10) / 500;

WARNING: simple_strtoul is obsolete, use kstrtoul instead
+	unsigned long temp = simple_strtoul(buf, NULL, 10) / 500;

Signed-off-by: Frans Meulenbroeks <fransmeulenbroeks@gmail.com>
Acked-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>