iio: adc: ad799x: leave sysfs naming to the core

This shouldn't change anything since the core calls the events folder
"events" anyways.

Signed-off-by: Martin Kepplinger <martink@posteo.de>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>