[XFS] fix compilation without CONFIG_PROC_FS

SGI-PV: 984019

SGI-Modid: xfs-linux-melb:xfs-kern:31408a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tim Shimmin <tes@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>