time: ntp: refactor up ntp_update_frequency()

Impact: cleanup, no functionality changed

Change ntp_update_frequency() from a hard to follow code
flow that uses global variables as temporaries, to a clean
input+output flow.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/time/ntp.c

@@ -83,27 +83,24 @@ static long			ntp_tick_adj;
  */
 static void ntp_update_frequency(void)
 {
-	u64 prev_base;
 	u64 second_length;
-
-	prev_base = tick_length_base;
+	u64 new_base;
 
 	second_length		 = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
 						<< NTP_SCALE_SHIFT;
 
 	second_length		+= (s64)ntp_tick_adj << NTP_SCALE_SHIFT;
 	second_length		+= time_freq;
 
-	tick_length_base	 = second_length;
-
 	tick_nsec		 = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
-	tick_length_base	 = div_u64(tick_length_base, NTP_INTERVAL_FREQ);
+	new_base		 = div_u64(second_length, NTP_INTERVAL_FREQ);
 
 	/*
 	 * Don't wait for the next second_overflow, apply
-	 * the change to the tick length immediately
+	 * the change to the tick length immediately:
 	 */
-	tick_length		+= tick_length_base - prev_base;
+	tick_length		+= new_base - tick_length_base;
+	tick_length_base	 = new_base;
 }
 
 static void ntp_update_offset(long offset)