NTFS: - Use i_size_read() in fs/ntfs/super.c once and then use the cached

	value afterwards.  Cache the initialized_size in the same way and
	protect access to the two sizes using the size_lock.
      - Minor optimization to fs/ntfs/super.c::ntfs_statfs() and its helpers.

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