dma-mapping: benchmark: avoid needless copy_to_user if benchmark fails

If do_map_benchmark() has failed, there is nothing useful to copy back
to userspace.

Suggested-by: Barry Song <[email protected]>
Signed-off-by: Fedor Pchelkin <[email protected]>
Acked-by: Robin Murphy <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

Author: pchelkin91

kernel/dma/map_benchmark.c

@@ -256,6 +256,9 @@ static long map_benchmark_ioctl(struct file *file, unsigned int cmd,
 		 * dma_mask changed by benchmark
 		 */
 		dma_set_mask(map->dev, old_dma_mask);
+
+		if (ret)
+			return ret;
 		break;
 	default:
 		return -EINVAL;