[media] em28xx-video: Swap release order to avoid lock nesting

vb2_fop_release might take the video queue mutex lock.
In order to avoid nesting mutexes the private mutex is taken after the
fop_release has finished.
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/usb/em28xx/em28xx-video.c

@@ -1664,8 +1664,8 @@ static int em28xx_v4l2_close(struct file *filp)
 
 	em28xx_videodbg("users=%d\n", dev->users);
 
-	mutex_lock(&dev->lock);
 	vb2_fop_release(filp);
+	mutex_lock(&dev->lock);
 
 	if (dev->users == 1) {
 		/* the device is already disconnect,