time: Export set_normalized_timespec.

Sorry I have just realized set_normalized_timespec() (used in
timespec_sub()) is not exported, and link will fail because of it...
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/time.c

@@ -379,6 +379,7 @@ void set_normalized_timespec(struct timespec *ts, time_t sec, long nsec)
 	ts->tv_sec = sec;
 	ts->tv_nsec = nsec;
 }
+EXPORT_SYMBOL(set_normalized_timespec);
 
 /**
  * ns_to_timespec - Convert nanoseconds to timespec