iio: light: apds9960: Fix iio_event_spec structures

There is only one interrupt enable option for both ALS low and high
thresholds, and one for both Proximity low and high thresholds.

Signed-off-by: Subhajit Ghosh <subhajit.ghosh@vixtechnology.com>
Reviewed-by: Matt Ranostay <matt.ranostay@konsulko.com>
Link: https://lore.kernel.org/r/20221110101241.10576-1-subhajit.ghosh@vixtechnology.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>