sched: Fix up attr::sched_priority warning

Fengguang Wu reported the following build warning:

  > kernel/sched/core.c:3067 __sched_setscheduler() warn: unsigned 'attr->sched_priority' is never less than zero.

Since it doesn't make sense for attr::sched_priority to be negative,
remove the check, since we already test for an upper limit any actual
negative values passed in through the old param::sched_priority field
will still be detected.
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Dario Faggioli <raistlin@linux.it>
Fixes: d50dde5a ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI")
Link: http://lkml.kernel.org/n/tip-fid9nalzii2r5voxtf4eh5kz@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -3282,8 +3282,7 @@ static int __sched_setscheduler(struct task_struct *p,
 	 * 1..MAX_USER_RT_PRIO-1, valid priority for SCHED_NORMAL,
 	 * SCHED_BATCH and SCHED_IDLE is 0.
 	 */
-	if (attr->sched_priority < 0 ||
-	    (p->mm && attr->sched_priority > MAX_USER_RT_PRIO-1) ||
+	if ((p->mm && attr->sched_priority > MAX_USER_RT_PRIO-1) ||
 	    (!p->mm && attr->sched_priority > MAX_RT_PRIO-1))
 		return -EINVAL;
 	if ((dl_policy(policy) && !__checkparam_dl(attr)) ||