staging:iio:adis16400 replace unnecessary event line registration.

Whilst the adis16400 does indeed support events, currently the driver
does not.  The trigger code should never use that infrastructure.

Tested indirectly via the IMU driver merge to follow.

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>