timekeeping: Simplify tai updating from do_adjtimex

Since we are taking the timekeeping locks, just go ahead
and update any tai change directly, rather then dropping
the lock and calling a function that will just take it again.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>

kernel/time/timekeeping.c

@@ -1618,9 +1618,10 @@ EXPORT_SYMBOL_GPL(ktime_get_monotonic_offset);
  */
 int do_adjtimex(struct timex *txc)
 {
+	struct timekeeper *tk = &timekeeper;
 	unsigned long flags;
 	struct timespec ts;
-	s32 tai, orig_tai;
+	s32 tai;
 	int ret;
 
 	/* Validate the data before disabling interrupts */
@@ -1640,19 +1641,17 @@ int do_adjtimex(struct timex *txc)
 	}
 
 	getnstimeofday(&ts);
-	orig_tai = tai = timekeeping_get_tai_offset();
 
 	raw_spin_lock_irqsave(&timekeeper_lock, flags);
 	write_seqcount_begin(&timekeeper_seq);
 
+	tai = tk->tai_offset;
 	ret = __do_adjtimex(txc, &ts, &tai);
 
+	__timekeeping_set_tai_offset(tk, tai);
 	write_seqcount_end(&timekeeper_seq);
 	raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
 
-	if (tai != orig_tai)
-		timekeeping_set_tai_offset(tai);
-
 	return ret;
 }