iio: adc: max1118: Use devm_ managed functions for all of probe

This simplifies error handling and allows us to drop the remove
function entirely.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Alexandru Ardelean <aardelean@deviqon.com>
Link: https://lore.kernel.org/r/20210516172520.1398835-4-jic23@kernel.org