CIFS: Fix wrong buffer pointer usage in smb_set_file_info

Commit 6bdf6dbd caused a regression
in setattr codepath that leads to files with wrong attributes.

Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>