hwmon: (max6639) Update Datasheet URL

The old Datasheet does not exist anymore.

Signed-off-by: Marcello Sylvester Bauer <sylv@sylv.io>
Link: https://lore.kernel.org/r/76025f40d2684dc0d3ec02c8899b726b07a0e7da.1643299570.git.sylv@sylv.io


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