iio: chemical: sps30: fix missing triggered buffer dependency

SPS30 uses triggered buffer, but the dependency is not specified in the
Kconfig file.  Fix this by selecting IIO_BUFFER and IIO_TRIGGERED_BUFFER
config symbols.

Cc: stable@vger.kernel.org
Fixes: 232e0f6d

 ("iio: chemical: add support for Sensirion SPS30 sensor")
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>