selftests/memfd/memfd_test: fix possible NULL pointer dereference

If `name' is NULL, a NULL pointer may be accessed in printf.

Link: https://lkml.kernel.org/r/20250114032115.58638-1-liuye@kylinos.cn
Signed-off-by: liuye <liuye@kylinos.cn>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: "Isaac J. Manjarres" <isaacmanjarres@google.com>
Cc: Jeff Xu <jeffxu@google.com>
Cc: Saurav Shah <sauravshah.31@gmail.com>
Cc: Shuah Khan (Samsung OSG) <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: qiyeliu

tools/testing/selftests/memfd/memfd_test.c

@@ -171,7 +171,7 @@ static void mfd_fail_new(const char *name, unsigned int flags)
 	r = sys_memfd_create(name, flags);
 	if (r >= 0) {
 		printf("memfd_create(\"%s\", %u) succeeded, but failure expected\n",
-		       name, flags);
+		       name ? name : "NULL", flags);
 		close(r);
 		abort();
 	}