selftests/memfd/memfd_test: fix possible NULL pointer dereference

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>