V4L/DVB (9647): em28xx: void having two concurrent control URB's

Now that we have a polling task for IR, there's a race condition, since
IR can be polling while other operations are being doing. Also, we are
now sharing the same urb_buf for both read and write control urb
operations. So, we need a mutex.

Thanks to Davin Heitmueller <devin.heitmueller@gmail.com> for warning me.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/video/em28xx/em28xx-video.c b/drivers/media/video/em28xx/em28xx-video.c
index bca5955..c32fc7d 100644
--- a/drivers/media/video/em28xx/em28xx-video.c
+++ b/drivers/media/video/em28xx/em28xx-video.c
@@ -1936,6 +1936,7 @@
 
 	dev->udev = udev;
 	mutex_init(&dev->lock);
+	mutex_init(&dev->ctrl_urb_lock);
 	spin_lock_init(&dev->slock);
 	init_waitqueue_head(&dev->open);
 	init_waitqueue_head(&dev->wait_frame);