rcu: Use proper cpp macro for ->gp_flags

One of the ->gp_flags assignments used a raw number rather than the
cpp macro that was intended for this purpose, which this commit fixes.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcutree.c

@@ -1452,7 +1452,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
 	rdp = this_cpu_ptr(rsp->rda);
 	rcu_advance_cbs(rsp, rnp, rdp);  /* Reduce false positives below. */
 	if (cpu_needs_another_gp(rsp, rdp))
-		rsp->gp_flags = 1;
+		rsp->gp_flags = RCU_GP_FLAG_INIT;
 	raw_spin_unlock_irq(&rnp->lock);
 }