Input: sur40 - fix error return code

Propagate error code on failure, or upper layers will be confused by
returned 0 (success) code.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/sur40.c

@@ -581,6 +581,7 @@ static int sur40_probe(struct usb_interface *interface,
 	sur40->alloc_ctx = vb2_dma_sg_init_ctx(sur40->dev);
 	if (IS_ERR(sur40->alloc_ctx)) {
 		dev_err(sur40->dev, "Can't allocate buffer context");
+		error = PTR_ERR(sur40->alloc_ctx);
 		goto err_unreg_v4l2;
 	}