[XFS] kill xfs_freeze.

No need to have a wrapper just two call two more functions.

SGI-PV: 971186
SGI-Modid: xfs-linux-melb:xfs-kern:29816a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Donald Douwsma <donaldd@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>