[XFS] Fix sparse warnings in kmem_* functions Patch from Victor Fusco

<victor@cetuc.puc-rio.br>

SGI-PV: 940376
SGI-Modid: xfs-linux:xfs-kern:196705a

Signed-off-by: Christoph Hellwig <hch@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>