iio: srf08: fix link error "devm_iio_triggered_buffer_setup" undefined

commit 511051d5 upstream.

Functions for triggered buffer support are needed by this module.
If they are not defined accidentally by another driver, there's an error
thrown out while linking.

Add a select of IIO_BUFFER and IIO_TRIGGERED_BUFFER in the Kconfig file.

Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Fixes: a8319593 ("iio: srf08: add triggered buffer support")
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>