iio: accel: kxcjk-1013: Increment ref counter for indio_dev->trig

Assigning indio_dev->trig is not a good idea, as this can result in
wrong reference count for trigger device. If assigned, it is better to
increment reference counter by calling iio_trigger_get.
Refer to http://www.spinics.net/lists/linux-iio/msg13669.html for discussion
with Jonathan.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>