[CPUFREQ] fix up comment in cpufreq.h

Fix up comment in cpufreq.h stating transition latency should be passed
in microseconds -- it was decided long ago to switch to nanoseconds.
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Dave Jones <davej@redhat.com>

include/linux/cpufreq.h

@@ -49,7 +49,7 @@ int cpufreq_unregister_notifier(struct notifier_block *nb, unsigned int list);
 /* Frequency values here are CPU kHz so that hardware which doesn't run 
  * with some frequencies can complain without having to guess what per 
  * cent / per mille means. 
- * Maximum transition latency is in microseconds - if it's unknown,
+ * Maximum transition latency is in nanoseconds - if it's unknown,
  * CPUFREQ_ETERNAL shall be used.
  */