iio: vcnl4000: Fix i2c swapped word reading.

The bytes returned by the i2c reading need to be swapped
unconditionally. Otherwise, on be16 platforms, an incorrect value will be
returned.

Taking the slow path via next merge window as its been around a while
and we have a patch set dependent on this which would be held up.

Fixes: 62a1efb9 ("iio: add vcnl4000 combined ALS and proximity sensor")
Signed-off-by: Mathieu Othacehe <m.othacehe@gmail.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>