iio:cm36651: Convert to new event config interface

Switch the cm36651 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: Beomho Seo <beomho.seo@samsung.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>