Make i945/raminit.c:fsbclk() return u16 rather than int

Make i945/raminit.c:fsbclk() return u16 rather than int

This is needed for Gentoo gcc-4.1.2 to build the i945 code. A warning is
thrown because the comparison in the last hunk is between u16 and -1 and
can never be true.

Signed-off-by: Peter Stuge <peter@stuge.se>
Acked-by: Patrick Georgi <patrick.georgi@coresystems.de>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@5895 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1