rcu: Catch up rcu_report_qs_rdp() comment with reality

/*

 * Record a quiescent state for the specified CPU to that CPU's rcu_data

 * structure.  This must be either called from the specified CPU, or

 * called when the specified CPU is known to be offline (and when it is

 * also known that no other CPU is concurrently trying to help the offline

 * CPU).  The lastcomp argument is used to make sure we are still in the

 * grace period of interest.  We don't want to end the current grace period

 * based on quiescent states detected in an earlier grace period!

 * structure.  This must be called from the specified CPU.

 */

static void

rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)