staging:iio: tree wide IIO_RING_TRIGGERED -> IIO_BUFFER_TRIGGERED

also, IIO_RING_HARDWARE_BUFFER -> IIO_BUFFER_HARDWARE

These aren't always rings so the naming should not imply that.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>