rcu-tasks: Update comments to cond_resched_tasks_rcu_qs()

The cond_resched_rcu_qs() function no longer exists, despite being mentioned
several times in kernel/rcu/tasks.h.  This commit therefore updates it to
the current cond_resched_tasks_rcu_qs().

Reported-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>