ntfs_fill_super() and ntfs_read_inode_mount() cleaned up.  Removed
the kludges around the first iget() on NTFS.  Instead of playing with
(re)setting ->s_op we have the MFT_FILE inode set up by explicit new_inode()/
set ->i_ino/insert_inode_hash()/call ntfs_read_inode_mount() directly.
That kills the need of second super_operations and it allows to return
error from ntfs_read_inode_mount() without resorting to ugly "poisoning"
tricks.