sched/debug: Fix trival print_task() format

Ensure leave one space between state and task name.

w/o patch:
runnable tasks:
 S           task   PID         tree-key  switches  prio     wait
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200414125721.195801-1-xiexiuqi@huawei.com