hwmon: (adt7475) Change update functions to add error handling

I2C SMBus sometimes returns error codes.
In the error case, measurement values are updated incorrectly.
The sensor application then generates warning log messages and SNMP traps.
To prevent this, add error handling into the update functions.

Signed-off-by: Tokunori Ikegami <ikegami@allied-telesis.co.jp>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Chris Packham <chris.packham@alliedtelesis.co.nz>
[groeck: Update description]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>