[media] V4L2: mt9t031: don't Oops if asynchronous probing is attempted

The mt9t031 driver hasn't yet been updated to support asynchronous
subdevice probing. If such a probing is attempted, the driver is allowed
to fail, but it shouldn't Oops. This patch fixes such a potential NULL
pointer dereference.
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/i2c/soc_camera/mt9t031.c

@@ -594,9 +594,12 @@ static int mt9t031_s_power(struct v4l2_subdev *sd, int on)
 		ret = soc_camera_power_on(&client->dev, ssdd, mt9t031->clk);
 		if (ret < 0)
 			return ret;
-		vdev->dev.type = &mt9t031_dev_type;
+		if (vdev)
+			/* Not needed during probing, when vdev isn't available yet */
+			vdev->dev.type = &mt9t031_dev_type;
 	} else {
-		vdev->dev.type = NULL;
+		if (vdev)
+			vdev->dev.type = NULL;
 		soc_camera_power_off(&client->dev, ssdd, mt9t031->clk);
 	}