docs: hwmon: (ltc2945) update datasheet link

Old one isn't working anymore. Update to the latest datasheet link.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20201005131226.1774081-1-alexandru.ardelean@analog.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>