staging:iio:adis16203 replace unnecessary event line registration.

Whilst the adis16203 does indeed support events, currently the driver
does not.  The trigger code should never use that infrastructure.

Untested, but identical in form to those that have been so should be fine.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>