staging: vchiq_arm: Fix platform device unregistration

In error case platform_device_register_data would return an ERR_PTR
instead of NULL. So we better check this before unregistration.

Fixes: 37b7b30 ("staging/vc04_services: Register a platform device for the camera driver.")
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c

@@ -3578,7 +3578,8 @@ static int vchiq_probe(struct platform_device *pdev)
 
 static int vchiq_remove(struct platform_device *pdev)
 {
-	platform_device_unregister(bcm2835_camera);
+	if (!IS_ERR(bcm2835_camera))
+		platform_device_unregister(bcm2835_camera);
 	vchiq_debugfs_deinit();
 	device_destroy(vchiq_class, vchiq_devid);
 	cdev_del(&vchiq_cdev);