linux: fix condition for entering tickless state

I noticed that timer interrupts were running at full rate regardless
of whether the system was idle.
softlockup_get_next_event() must return the maximum of zero and the
delta to the next event, not the minimum (which is always zero or
negative, yielding zero or a very large positive number as return
value).

Signed-off-by: Jan Beulich <jbeulich@novell.com>

patches/linux-2.6.18/softlockup-no-idle-hz.patch

@@ -34,7 +34,7 @@ diff -pruN ../orig-linux-2.6.18/kernel/softlockup.c ./kernel/softlockup.c
 +			!per_cpu(watchdog_task, this_cpu))
 +		return MAX_JIFFY_OFFSET;
 +
-+	return min_t(long, 0, touch_timestamp + HZ - jiffies);
++	return max_t(long, 0, touch_timestamp + HZ - jiffies);
 +}
 +
  /*