iio: proximity: as3935: fix iio_trigger_poll issue

commit 9122b54f upstream.

Using iio_trigger_poll() can oops when multiple interrupts
happen before the first is handled.

Use iio_trigger_poll_chained() instead and use the timestamp
when processed, since it will be in theory be 2 ms max latency.

Fixes: 24ddb0e4 ("iio: Add AS3935 lightning sensor support")
Signed-off-by: Matt Ranostay <matt.ranostay@konsulko.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
[bwh: Backported to 3.16:
 - iio_get_time_ns() doesn't take any parameters
 - iio_trigger_poll{,_chained}() do take a time parameter]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/iio/proximity/as3935.c

@@ -215,7 +215,7 @@ static irqreturn_t as3935_trigger_handler(int irq, void *private)
 
 	st->buffer[0] = val & AS3935_DATA_MASK;
 	iio_push_to_buffers_with_timestamp(indio_dev, &st->buffer,
-					   pf->timestamp);
+					   iio_get_time_ns());
 err_read:
 	iio_trigger_notify_done(indio_dev->trig);
 
@@ -238,7 +238,7 @@ static void as3935_event_work(struct work_struct *work)
 
 	switch (val) {
 	case AS3935_EVENT_INT:
-		iio_trigger_poll(st->trig, iio_get_time_ns());
+		iio_trigger_poll_chained(st->trig, iio_get_time_ns());
 		break;
 	case AS3935_NOISE_INT:
 		dev_warn(&st->spi->dev, "noise level is too high");