staging:iio:adis16204 replace unnecessary event line registration.

Whilst the adis16204 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.

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>