iio:apds9300: Use new event config interface

Switch the apds9300 driver to the new IIO event config interface as the old one
is going to be removed.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Cc: Oleksandr Kravchenko <o.v.kravchenko@globallogic.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>