hwmon: Update documentation to clarify rules for the 'name' attribute

Clarify that the name attribute must report a valid name, and the rules
for valid names. Also clarify that the name parameter must be provided
for all supported API functions.

Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>