staging: iio: industrialio-trigger: set iio_poll_func private_data

Failure to set iio_poll_func private_data, causes zero pointer access
violations in all consumer trigger handlers.
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/iio/industrialio-trigger.c

@@ -294,6 +294,7 @@ struct iio_poll_func
 	pf->h = h;
 	pf->thread = thread;
 	pf->type = type;
+	pf->private_data = private;
 
 	return pf;
 }