The struct iio_dev .trig field is to be used only by the IIO core,
the driver shall not fill this field. This fixes ugly crash when
the driver is compiled as a module and the module is rmmod'd.
Signed-off-by: Marek Vasut <marex@denx.de> Cc: Fabio Estevam <fabio.estevam@freescale.com> Cc: Jonathan Cameron <jic23@kernel.org> Cc: Shawn Guo <shawn.guo@linaro.org> Signed-off-by: Jonathan Cameron <jic23@kernel.org>