hwmon: (sht3x) Add new non-stardard sysfs attribute

Add "repeatability" attribute to sysfs, it could be
read or written to control the sensor.

Signed-off-by: JuenKit Yip <JuenKit_Yip@hotmail.com>
Link: https://lore.kernel.org/r/DB4PR10MB6261B507C7656E3568DA33E39258A@DB4PR10MB6261.EURPRD10.PROD.OUTLOOK.COM


[groeck: Fixed multi-line alignment; dropped check of unsigned against < 0]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>