rcu: Simplify rcu_report_dead() call to rcu_report_exp_rdp()

Currently, rcu_report_dead() disables preemption across its call to
rcu_report_exp_rdp(), but this is pointless because interrupts are
already disabled by the caller.  In addition, rcu_report_dead() computes
the address of the outgoing CPU's rcu_data structure, which is also
pointless because this address is already present in local variable rdp.
This commit therefore drops the preemption disabling and passes rdp
to rcu_report_exp_rdp().
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/tree.c

@@ -4294,9 +4294,7 @@ void rcu_report_dead(unsigned int cpu)
 	do_nocb_deferred_wakeup(rdp);
 
 	/* QS for any half-done expedited grace period. */
-	preempt_disable();
-	rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
-	preempt_enable();
+	rcu_report_exp_rdp(rdp);
 	rcu_preempt_deferred_qs(current);
 
 	/* Remove outgoing CPU from mask in the leaf rcu_node structure. */