staging: iio: error case memory leak fix

The data pointer should be freed in the error
cases of adis16400_trigger_handler().

Signed-off-by: Andre Bartke <andre.bartke@gmail.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>