iio: proximity: as3935: fix iio_trigger_poll issue

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")
Cc: stable@vger.kernel.org
Signed-off-by: Matt Ranostay <matt.ranostay@konsulko.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>