iio: pressure: mprls0025pa fix off-by-one enum

Fix off-by-one error in transfer-function property.
The honeywell,transfer-function property takes values between 1-3 so
make sure the proper enum gets used.

Fixes: 713337d9 ("iio: pressure: Honeywell mprls0025pa pressure sensor")
Co-developed-by: Andreas Klinger <ak@it-klinger.de>
Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Signed-off-by: Petre Rodan <petre.rodan@subdimension.ro>
Link: https://lore.kernel.org/r/20231229092445.30180-5-petre.rodan@subdimension.ro


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>