fstests: add SPDX license comments for src/log-writes/*

I apparently never bothered to put copyright or license info with this
code, just tag it as GPL 2 and I'll fix the upstream stuff as well.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>

src/log-writes/log-writes.c

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #include <linux/fs.h>
 #include <sys/types.h>
 #include <sys/stat.h>

src/log-writes/log-writes.h

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef _LOG_WRITES_H_
 #define _LOG_WRITES_H_
 

src/log-writes/replay-log.c

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #include <stdio.h>
 #include <unistd.h>
 #include <getopt.h>