iio: hudmidity: hdc100x: fix incorrect shifting and scaling

Shifting sensor data to the right 2 bits was incorrect and caused the
scaling values + offsets to be invalid.

Reported-by: Alison Schofield <amsfield22@gmail.com>
Signed-off-by: Matt Ranostay <mranostay@gmail.com>
Tested-by: Alison Schofield <amsfield22@gmail.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>