[XFS] kill v_vfsp member from struct bhv_vnode

We can easily get at the vfsp through the super_block but it will soon be
gone anyway.

SGI-PV: 969608
SGI-Modid: xfs-linux-melb:xfs-kern:29494a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>