Mask root object ID into f_fsid in btrfs_statfs()

Date: Mon, 18 Aug 2008 13:10:20 +0100
This means that subvolumes get a different fsid, and NFS exporting them
works properly.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>