cached value everywhere.  Cache the initialized_size in the same way
	and protect the critical region where the two sizes are read using the
	new size_lock of the ntfs inode.
      - Add the new size_lock to the ntfs_inode structure (fs/ntfs/inode.h)
	and initialize it (fs/ntfs/inode.c).
Signed-off-by: NAnton Altaparmakov <aia21@cantab.net>