rcu: Eliminate rcu_state structure's ->call field

The rcu_state structure's ->call field references the corresponding RCU
flavor's call_rcu() function.  However, now that there is only ever one
rcu_state structure in a given build of the Linux kernel, and that flavor
uses plain old call_rcu(), there is not a lot of point in continuing to
have the ->call field.  This commit therefore removes it.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree.c

@@ -76,7 +76,6 @@ static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data);
 struct rcu_state rcu_state = {
 	.level = { &rcu_state.node[0] },
 	.rda = &rcu_data,
-	.call = call_rcu,
 	.gp_state = RCU_GP_IDLE,
 	.gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT,
 	.barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex),

kernel/rcu/tree.h

@@ -313,7 +313,6 @@ struct rcu_state {
 						/* Hierarchy levels (+1 to */
 						/*  shut bogus gcc warning) */
 	struct rcu_data __percpu *rda;		/* pointer of percu rcu_data. */
-	call_rcu_func_t call;			/* call_rcu() flavor. */
 	int ncpus;				/* # CPUs seen so far. */
 
 	/* The following fields are guarded by the root rcu_node's lock. */

kernel/rcu/tree_exp.h

@@ -619,7 +619,7 @@ static void _synchronize_rcu_expedited(struct rcu_state *rsp,
 
 	/* If expedited grace periods are prohibited, fall back to normal. */
 	if (rcu_gp_is_normal()) {
-		wait_rcu_gp(rsp->call);
+		wait_rcu_gp(call_rcu);
 		return;
 	}