media: usb: null check create_singlethread_workqueue

In sd_start return value of create_singlethread_workqueue needs null
check.

Signed-off-by: Navid Emamdoost <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/usb/gspca/sq905.c

···
 	}
 	/* Start the workqueue function to do the streaming */
 	dev->work_thread = create_singlethread_workqueue(MODULE_NAME);
+	if (!dev->work_thread)
+		return -ENOMEM;
+
 	queue_work(dev->work_thread, &dev->work_struct);
 
 	return 0;