hwmon: (iio_hwmon) fix memory leak in name attribute

The "name" variable's memory is now freed when the device is destructed
thanks to devm function.

Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Reported-by: Guenter Roeck <linux@roeck-us.net>
Fixes: e0f8a24e ("staging:iio::hwmon interface client driver.")
Fixes: 61bb53bc

 ("hwmon: (iio_hwmon) Add support for humidity sensors")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>