hwmon: (max6650) Improve error handling in max6650_update_device

Pass errors from i2c_smbus_read_byte_data() back to the caller of
max6650_update_device().

Cc: Jean-Francois Dagenais <jeff.dagenais@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>