[XFS] Quota inode has no parent.

Avoid using a special "zero inode" as the parent of the quota inode as
this can confuse the filestreams code into thinking the quota inode has a
parent. We do not want the quota inode to follow filestreams allocation
rules, so pass a NULL as the parent inode and detect this condition when
doing stream associations.

SGI-PV: 964469
SGI-Modid: xfs-linux-melb:xfs-kern:29098a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>