smb/client: fix nlink of an overwritten open file

Reproducer:

  1. server: systemctl start ksmbd
  2. client: mount with `posix` option
     mount -t cifs -o posix //${server_ip}/export /mnt
  3. client: touch /mnt/file1 /mnt/file2
  4. client: C program: int fd = open("/mnt/file2", O_RDONLY);
  5. client: C program: rename("/mnt/file1", "/mnt/file2");
  6. client: C program: struct stat stbuf; fstat(fd, &stbuf);
                        stbuf.st_nlink is 1, should be 0

This patch fixes xfstests generic/035 when mounted with `posix` option.

Signed-off-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>