memfd_test: Add missing argument to printf()

Add a missing path argument buf to printf()
Signed-off-by: NPranith Kumar <bobby.prani@gmail.com>
Reviewed-by: NDavid Herrmann <dh.herrmann@gmail.com>
Signed-off-by: NShuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/memfd/memfd_test.c

@@ -203,7 +203,7 @@ static void mfd_fail_open(int fd, int flags, mode_t mode)
 	sprintf(buf, "/proc/self/fd/%d", fd);
 	r = open(buf, flags, mode);
 	if (r >= 0) {
-		printf("open(%s) didn't fail as expected\n");
+		printf("open(%s) didn't fail as expected\n", buf);
 		abort();
 	}
 }