Input: ims-pcu - sanity check against missing interfaces

A malicious device missing interface can make the driver oops.
Add sanity checking.

Signed-off-by: Oliver Neukum <ONeukum@suse.com>
CC: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
static void ims_pcu_destroy_backlight(struct ims_pcu *pcu)
{
	struct ims_pcu_backlight *backlight = &pcu->backlight;

	led_classdev_unregister(&backlight->cdev);
	cancel_work_sync(&backlight->work);
}

static void ims_pcu_destroy_backlight(struct ims_pcu *pcu)
{
	struct ims_pcu_backlight *backlight = &pcu->backlight;

	led_classdev_unregister(&backlight->cdev);
	cancel_work_sync(&backlight->work);
}
