[media] media: omap3isp: fix a potential NULL deref

Fix a potential NULL pointer dereference by skipping registration of
external entities in case none are provided.

This is useful at least when testing mere memory-to-memory scenarios.
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/omap3isp/isp.c

@@ -1748,7 +1748,7 @@ static int isp_register_entities(struct isp_device *isp)
 		goto done;
 
 	/* Register external entities */
-	for (subdevs = pdata->subdevs; subdevs->subdevs; ++subdevs) {
+	for (subdevs = pdata->subdevs; subdevs && subdevs->subdevs; ++subdevs) {
 		struct v4l2_subdev *sensor;
 		struct media_entity *input;
 		unsigned int flags;