[PATCH] fix outdated comment in jiffies.h

From: Tim Schmielau <tim@physik3.uni-rostock.de>

include/linux/jiffies.h

@@ -10,7 +10,7 @@
 
 /*
  * The 64-bit value is not volatile - you MUST NOT read it
- * without holding read_lock_irq(&xtime_lock).
+ * without sampling the sequence number in xtime_lock.
  * get_jiffies_64() will do this for you as appropriate.
  */
 extern u64 jiffies_64;