x86: fix cpufreq + sched_clock() regression

I noticed that my sched_clock() was slow on a number of machine, so I
started looking at cpufreq.

The below seems to fix the problem for me.

Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/kernel/tsc.c

···
 			mark_tsc_unstable("cpufreq changes");
 	}
 
-	set_cyc2ns_scale(tsc_khz_ref, freq->cpu);
+	set_cyc2ns_scale(tsc_khz, freq->cpu);
 
 	return 0;
 }