[XFS] reducing the number of random number functions.

Patch provided by Joe Perches

SGI-PV: 961696
SGI-Modid: xfs-linux-melb:xfs-kern:28209a

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>