Add support for medium repeatability.

Per datasheet:

The stated repeatability is 3 times the standard deviation (3σ)
of multiple consecutive measurements at the stated repeatability
and at constant ambient conditions. It is a measure for the noise
on the physical sensor output. Different measurement modes allow
for high/medium/low repeatability.

For the humidity sensor, repeatability is documented as
0.25% RH for low repeatability, 0.15% RH for medium repeatability,
and 0.10% RH for high repeatability. Support all three modes.
Signed-off-by: JuenKit Yip <JuenKit_Yip@hotmail.com>
Link: https://lore.kernel.org/r/DB4PR10MB6261A70CD0444248ADDCC3219258A@DB4PR10MB6261.EURPRD10.PROD.OUTLOOK.COM
[groeck: Added details to description]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>