rcu/tasks: Update rtp->tasks_gp_seq comment

The rtp->tasks_gp_seq grace-period sequence number is not a strict count,
but rather the usual RCU sequence number with the lower few bits tracking
per-grace-period state and the upper bits the count of grace periods
since boot, give or take the initial value.  This commit therefore
adjusts this comment.
Signed-off-by: "Paul E. McKenney" <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>

kernel/rcu/tasks.h

@@ -65,7 +65,7 @@ struct rcu_tasks_percpu {
  * @init_fract: Initial backoff sleep interval.
  * @gp_jiffies: Time of last @gp_state transition.
  * @gp_start: Most recent grace-period start in jiffies.
- * @tasks_gp_seq: Number of grace periods completed since boot.
+ * @tasks_gp_seq: Number of grace periods completed since boot in upper bits.
  * @n_ipis: Number of IPIs sent to encourage grace periods to end.
  * @n_ipis_fails: Number of IPI-send failures.
  * @kthread_ptr: This flavor's grace-period/callback-invocation kthread.