src/: add license and copyright info to files

Add copyright and license info to files that I've authored in src/.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>

src/t_ext4_dax_inline_corruption.c

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2018 Intel Corporation. */
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>

src/t_ext4_dax_journal_corruption.c

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2018 Intel Corporation. */
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>

src/t_mmap_cow_race.c

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2017 Intel Corporation. */
 #include <errno.h>
 #include <fcntl.h>
 #include <libgen.h>

src/t_mmap_stale_pmd.c

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2017 Intel Corporation. */
 #include <errno.h>
 #include <fcntl.h>
 #include <libgen.h>