staging:iio:adt7316 get rid of legacy event handling code.

Note this driver is still a long way from being abi compliant.
What I have done here cleans up a few corners, but primarily gets
it away from using the infrastructure that is going away.

Untested
Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>