- Remove nr_mft_bits and the now superfluous union with nr_mft_records
  from ntfs_volume structure.
- Remove nr_lcn_bits and the now superfluous union with nr_clusters
  from ntfs_volume structure.
- Use iget5_locked() and friends instead of conventional iget(). Wrap
  the call in fs/ntfs/inode.c::ntfs_iget() and update callers of iget()
  to use ntfs_iget(). Leave only one iget() call at mount time so we
  don't need an ntfs_iget_mount().
- Change fs/ntfs/inode.c::ntfs_new_extent_inode() to take mft_no as an
  additional argument.