sched/debug: Avoid checking in_atomic_preempt_off() twice in schedule_debug()

in_atomic_preempt_off() already gets called in schedule_debug() once,
which is the only caller of __schedule_bug().

Skip the second call within __schedule_bug(), it should always be true
at this point.

[ mingo: Clarified the changelog. ]

Signed-off-by: Liming Wu <liming.wu@jaguarmicro.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230825023501.1848-1-liming.wu@jaguarmicro.com