rcu: Remove redundant check of cpu_online()

Because invoke_cpu_core() checks whether the current CPU is online,
there is no need for __call_rcu_core() to redundantly check it.
There should not be any performance degradation because the called
function is visible to the compiler.  This commit therefore removes
the redundant check.
Signed-off-by: NYao Dongdong <yaodongdong@huawei.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree.c

@@ -2741,7 +2741,7 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
 	 * If called from an extended quiescent state, invoke the RCU
 	 * core in order to force a re-evaluation of RCU's idleness.
 	 */
-	if (!rcu_is_watching() && cpu_online(smp_processor_id()))
+	if (!rcu_is_watching())
 		invoke_rcu_core();
 
 	/* If interrupts were disabled or CPU offline, don't invoke RCU core. */