iio: Deselect IIO_TRIGGER for IIO_KFIFO_BUF

iio kfifo can be used without trigger support so there is no need to build it.

Signed-off-by: Karol Wrona <k.wrona@samsung.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>