Add SPDX license identifiers

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/test/openat2.c b/test/openat2.c
index 462bc9b..197821a 100644
--- a/test/openat2.c
+++ b/test/openat2.c
@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: MIT */
 /*
  * Description: run various openat(2) tests
  *