timekeeping: Fix timezone update

commit 64ce4c2f (time: Clean up warp_clock()) breaks the timezone
update in a very subtle way. To avoid the direct access to timekeeping
internals it adds the timezone delta to the current time with
timespec_add_safe(). This works nicely when the timezone delta is > 0.
If timezone delta is < 0 then the wrap check in timespec_add_safe()
triggers and timespec_add_safe() returns TIME_MAX and screws up
timekeeping completely. 

The comment above timespec_add_safe() says:
    It's assumed that both values are valid (>= 0)

Add the timezone seconds adjustment directly.
Reported-by: Rafael J. Wysocki <rjw@sisk.pl>
Tested-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/time.c

@@ -132,10 +132,10 @@ SYSCALL_DEFINE2(gettimeofday, struct timeval __user *, tv,
  */
 static inline void warp_clock(void)
 {
-	struct timespec delta, adjust;
-	delta.tv_sec = sys_tz.tz_minuteswest * 60;
-	delta.tv_nsec = 0;
-	adjust = timespec_add_safe(current_kernel_time(), delta);
+	struct timespec adjust;
+
+	adjust = current_kernel_time();
+	adjust.tv_sec += sys_tz.tz_minuteswest * 60;
 	do_settimeofday(&adjust);
 }