[CPUFREQ] Fix build failure on x86-64

arch/x86_64/kernel/cpufreq/../../../i386/kernel/cpu/cpufreq/speedstep-lib.c:131: error: 'MSR_FSB_FREQ' undeclared (first use in this function)

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Dave Jones <davej@redhat.com>