ntb_perf: Fix an error code in perf_copy_chunk()

We accidentally return success if dmaengine_submit() fails.  The fix is
to preserve the error code from dma_submit_error().
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Acked-by: NSerge Semin <fancer.lancer@gmail.com>
Signed-off-by: NJon Mason <jdmason@kudzu.us>

drivers/ntb/test/ntb_perf.c

@@ -828,7 +828,8 @@ static int perf_copy_chunk(struct perf_thread *pthr,
 	tx->callback_param = pthr;
 	dma_set_unmap(tx, unmap);
 
-	if (dma_submit_error(dmaengine_submit(tx))) {
+	ret = dma_submit_error(dmaengine_submit(tx));
+	if (ret) {
 		dmaengine_unmap_put(unmap);
 		goto err_free_resource;
 	}