iio: adc: palmas: Take probe fully device managed.

Review of a recent fix highlighted that this driver could be trivially
converted to be entirely devm managed.

That fix should be applied to resolve the fix in a fashion easy to back port
even though this change removes the relevant code.

[1] https://patchwork.kernel.org/project/linux-iio/patch/20230313205029.1881745-1-risca@dalakolonin.se/



Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Tested-by: Patrik Dahlström <risca@dalakolonin.se>
Reviewed-by: Patrik Dahlström <risca@dalakolonin.se>
Link: https://lore.kernel.org/r/20230318163039.56115-1-jic23@kernel.org