IIO: Documentation: Replace deprecated :c:func: Usage

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* struct :c:type:`iio_dev` - industrial I/O device

* :c:func:`iio_device_alloc()` - allocate an :c:type:`iio_dev` from a driver

* :c:func:`iio_device_free()` - free an :c:type:`iio_dev` from a driver

* :c:func:`iio_device_register()` - register a device with the IIO subsystem

* :c:func:`iio_device_unregister()` - unregister a device from the IIO

* iio_device_alloc() - allocate an :c:type:`iio_dev` from a driver

* iio_device_free() - free an :c:type:`iio_dev` from a driver

* iio_device_register() - register a device with the IIO subsystem

* iio_device_unregister() - unregister a device from the IIO

  subsystem

An IIO device usually corresponds to a single hardware sensor and it

At probe:

1. Call :c:func:`iio_device_alloc()`, which allocates memory for an IIO device.

1. Call iio_device_alloc(), which allocates memory for an IIO device.

2. Initialize IIO device fields with driver specific information (e.g.

   device name, device channels).

3. Call :c:func:`iio_device_register()`, this registers the device with the

3. Call iio_device_register(), this registers the device with the

   IIO core. After this call the device is ready to accept requests from user

   space applications.

At remove, we free the resources allocated in probe in reverse order:

1. :c:func:`iio_device_unregister()`, unregister the device from the IIO core.

2. :c:func:`iio_device_free()`, free the memory allocated for the IIO device.

1. iio_device_unregister(), unregister the device from the IIO core.

2. iio_device_free(), free the memory allocated for the IIO device.

IIO device sysfs interface

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