sched: fix warning in hrtick_start_fair()

Benjamin Herrenschmidt reported:

> I get that on ppc64 ...
>
> In file included from kernel/sched.c:1595:
> kernel/sched_fair.c: In function ‘hrtick_start_fair’:
> kernel/sched_fair.c:902: warning: comparison of distinct pointer types lacks a cast
>
> Probably harmless but annoying.

s64 delta = slice - ran;

-->	delta = max(10000LL, delta);

Probably ppc64's s64 is long vs long long..

I think hpa was looking at sanitizing all these 64bit types across the
architectures.

Use max_t with an explicit type meanwhile.
Reported-by: Benjamin Herrenschmid <benh@kernel.crashing.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched_fair.c

@@ -899,7 +899,7 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
 		 * doesn't make sense. Rely on vruntime for fairness.
 		 */
 		if (rq->curr != p)
-			delta = max(10000LL, delta);
+			delta = max_t(s64, 10000LL, delta);
 
 		hrtick_start(rq, delta);
 	}