Sign extend AD4170 data when channels are in bipolar configuration

[machschmitt]

According to reports, "the AD4170 drivers don't do a sign extension when reading the ADC registers, as the ADC is 24 bits, but the int variable is 32-bit, it fills the 4th bit with zeroes even if bit 23 is 1."

The ADC output code is two's complement when the channel setup has the bipolar field configured in the AFE register. Sign extend ADC data when the channel is in bipolar configuration.

[CLAassistant]

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