iio: ABI: add note about configuring other attributes during buffer capture

iio: ABI: add note about configuring other attributes during buffer capture

It might be impossible to configure other attributes (e.g.: events, scale,
sampling rate) if they impact the currently active buffer capture session.

On ADXL367, writing to register before 0x2E requires the device to be
placed in standby mode, otherwise the changes might be effective for
only part of a measurement.

To ensure this requirement, the configuration attributes of the IIO
device try to claim direct mode before switching to standby mode.
During a buffer capture, direct mode cannot be claimed, and the
attribute write callback returns -EBUSY.

Describe this behavior in the buffer/enable attribute description.

Signed-off-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
Link: https://lore.kernel.org/r/20220214073810.781016-4-cosmin.tanislav@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>