iio: adc: imx93_adc: load calibrated values even calibration failed

iio: adc: imx93_adc: load calibrated values even calibration failed

ADC calibration might fail because of the noise on reference voltage.
To avoid calibration fail, need to meet the following requirement:
    ADC reference voltage Noise < 1.8V * 1/2^ENOB

For the case which the ADC reference voltage on board do not meet
the requirement, still load the calibrated values, so ADC can also
work but maybe not that accurate.

Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Primoz Fiser <primoz.fiser@norik.com>
Link: https://patch.msgid.link/20250812-adc-v2-2-0260833f13b8@nxp.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>