NTFS: Change the mount options {u,f,d}mask to always parse the number as

NTFS: Change the mount options {u,f,d}mask to always parse the number as
      an octal number to conform to how chmod(1) works, too.  Thanks to
      Giuseppe Bilotta and Horst von Brand for pointing out the errors of
      my ways.

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