sched: Fix up attr::sched_priority warning

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: Fengguang Wu <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Cc: Juri Lelli <[email protected]>
Cc: Dario Faggioli <[email protected]>
Fixes: d50dde5a10f3 ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI")
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>