iio: temperature: tmp007: use device-managed functions in probe

iio: temperature: tmp007: use device-managed functions in probe

This change converts the driver to use device-managed functions in the
probe function. The power-down call is handled now via a
devm_add_action_or_reset() hook, and then devm_iio_device_register() can be
used to register the IIO device.

The final aim here would be for IIO to export only the device-managed
functions of it's API. That's a long way to go and this a small step in
that direction.

Signed-off-by: Alexandru Ardelean <aardelean@deviqon.com>
Link: https://lore.kernel.org/r/20210310093800.45822-1-aardelean@deviqon.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>