hwmon: (lm78/w83781d) Probe fewer I2C addresses

We've never seen any device supported by the lm78 or w83781d driver at
addresses 0x20-0x27, so let's stop probing these addresses. Extra probes cost
time, and have potential for confusing or misdetecting other I2C devices.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>