rcu: Update __call_rcu() comments

The __call_rcu() function's header comment refers to a cpu argument
that no longer exists, and the comment of the return path from
rcu_nocb_try_bypass() ignores the non-no-CBs CPU case.  This commit
therefore update both comments.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/tree.c

@@ -2642,12 +2642,7 @@ static void check_cb_ovld(struct rcu_data *rdp)
 	raw_spin_unlock_rcu_node(rnp);
 }
 
-/*
- * Helper function for call_rcu() and friends.  The cpu argument will
- * normally be -1, indicating "currently running CPU".  It may specify
- * a CPU only if that CPU is a no-CBs CPU.  Currently, only rcu_barrier()
- * is expected to specify a CPU.
- */
+/* Helper function for call_rcu() and friends.  */
 static void
 __call_rcu(struct rcu_head *head, rcu_callback_t func)
 {
@@ -2688,7 +2683,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func)
 	check_cb_ovld(rdp);
 	if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags))
 		return; // Enqueued onto ->nocb_bypass, so just leave.
-	/* If we get here, rcu_nocb_try_bypass() acquired ->nocb_lock. */
+	// If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock.
 	rcu_segcblist_enqueue(&rdp->cblist, head);
 	if (__is_kfree_rcu_offset((unsigned long)func))
 		trace_rcu_kfree_callback(rcu_state.name, head,