NTFS: Fix compilation when configured read-only.

- Add ifdef NTFS_RW around write specific code if fs/ntfs/runlist.[hc] and
  fs/ntfs/attrib.[hc].
- Minor bugfix to fs/ntfs/attrib.c::ntfs_attr_make_non_resident() where the
  runlist was not freed in all error cases.
- Add fs/ntfs/runlist.[hc]::ntfs_rl_find_vcn_nolock().

Signed-off-by: Anton Altaparmakov <aia21@cantab.net>