iio: core: use INDIO_ALL_BUFFER_MODES in iio_buffer_enabled()

This replaces use of individual buffer mode flags with
INDIO_ALL_BUFFER_MODES in the iio_buffer_enabled() function.

This simplifies the code and makes it robust in case of the addition of
new buffer modes.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20240108200647.3916681-1-dlechner@baylibre.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>