NTFS: - In fs/ntfs/compress.c, use i_size_read() at the start and then use the

NTFS: - In fs/ntfs/compress.c, use i_size_read() at the start and then use the
	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: Anton Altaparmakov <aia21@cantab.net>