[media] vb2: return ENOBUFS in start_streaming in case of too few buffers

This works together with the retry_start_streaming mechanism to allow userspace
to start streaming even if not all required buffers have been queued.

Signed-off-by: Hans Verkuil <[e-mail]>
Acked-by: Lad, Prabhakar <[e-mail]>
Cc: Tomasz Stanislawski <[e-mail]>
Cc: Kyungmin Park <[e-mail]>
Acked-by: Kamil Debski <[e-mail]>
Acked-by: Guennadi Liakhovetski <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/platform/davinci/vpbe_display.c

···
 	/* If buffer queue is empty, return error */
 	if (list_empty(&layer->dma_queue)) {
 		v4l2_err(&vpbe_dev->v4l2_dev, "buffer queue is empty\n");
-		return -EINVAL;
+		return -ENOBUFS;
 	}
 	/* Get the next frame from the buffer queue */
 	layer->next_frm = layer->cur_frm = list_entry(layer->dma_queue.next,

drivers/media/platform/davinci/vpif_capture.c

···
 	if (list_empty(&common->dma_queue)) {
 		spin_unlock_irqrestore(&common->irqlock, flags);
 		vpif_dbg(1, debug, "buffer queue is empty\n");
-		return -EIO;
+		return -ENOBUFS;
 	}
 
 	/* Get the next frame from the buffer queue */

drivers/media/platform/davinci/vpif_display.c

···
 	if (list_empty(&common->dma_queue)) {
 		spin_unlock_irqrestore(&common->irqlock, flags);
 		vpif_err("buffer queue is empty\n");
-		return -EIO;
+		return -ENOBUFS;
 	}
 
 	/* Get the next frame from the buffer queue */

drivers/media/platform/s5p-mfc/s5p_mfc_enc.c

···
 		if (ctx->src_bufs_cnt < ctx->pb_count) {
 			mfc_err("Need minimum %d OUTPUT buffers\n",
 					ctx->pb_count);
-			return -EINVAL;
+			return -ENOBUFS;
 		}
 	}
 

drivers/media/platform/s5p-tv/mixer_video.c

···
 
 	if (count == 0) {
 		mxr_dbg(mdev, "no output buffers queued\n");
-		return -EINVAL;
+		return -ENOBUFS;
 	}
 
 	/* block any changes in output configuration */

drivers/media/platform/soc_camera/mx2_camera.c

···
 	unsigned long flags;
 
 	if (count < 2)
-		return -EINVAL;
+		return -ENOBUFS;
 
 	spin_lock_irqsave(&pcdev->lock, flags);
 

drivers/staging/media/davinci_vpfe/vpfe_video.c

···
 	unsigned long addr;
 	int ret;
 
+	if (count == 0)
+		return -ENOBUFS;
 	ret = mutex_lock_interruptible(&video->lock);
 	if (ret)
 		goto streamoff;