hwmon: (ds1621) Fix checkpatch issues

Fixed:
ERROR: code indent should use tabs where possible
ERROR: do not use assignment in if condition
ERROR: trailing whitespace
WARNING: labels should not be indented
WARNING: please, no spaces at the start of a line
WARNING: simple_strtol is obsolete, use kstrtol instead

Also modified multi-line comments to follow Documentation/CodingStyle.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Jean Delvare <khali@linux-fr.org>