tools/runqslower: Use __state instead of state

Commit 2f064a59 ("sched: Change task_struct::state") renamed task->state
to task->__state in task_struct. Fix runqslower to use the new name of the
field.

Fixes: 2f064a59 ("sched: Change task_struct::state")
Signed-off-by: SanjayKumar Jeyakumar <vjsanjay@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210707052914.21473-1-vjsanjay@gmail.com