power: supply: twl4030_madc: Use devm_iio_channel_get() helper

Use the device lifecycle managed get function. This helps prevent
mistakes like releasing out of order in cleanup functions and
forgetting to release on error paths.

Signed-off-by: Andrew Davis <afd@ti.com>
Link: https://lore.kernel.org/r/20240123163653.384385-21-afd@ti.com


Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>