hwmon: Use i2c_smbus_{read,write}_word_swapped

Make use of the new i2c_smbus_{read,write}_word_swapped functions.
This makes the driver code more compact and readable. It also ensures
proper error handling.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Acked-by: Guenter Roeck <guenter.roeck@ericsson.com>
Cc: Dirk Eibach <eibach@gdsys.de>
Cc: "Mark M. Hoffman" <mhoffman@lightlink.com>
Cc: Guillaume Ligneul <guillaume.ligneul@gmail.com>