Use IHOLD(ip) instead of VN_HOLD(VFS_I(ip)).

SGI-PV: 981498

SGI-Modid: xfs-linux-melb:xfs-kern:31765a
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>