cfq-iosched: separate out cfqg_stats_reset() from cfq_pd_reset_stats()

Separate out cfqg_stats_reset() which takes struct cfqg_stats * from
cfq_pd_reset_stats() and move the latter to where other pd methods are
defined.  cfqg_stats_reset() will be used to implement hierarchical
stats.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>

block/cfq-iosched.c

@@ -688,11 +688,9 @@ static inline void cfqg_stats_update_completion(struct cfq_group *cfqg,
 				io_start_time - start_time);
 }
 
-static void cfq_pd_reset_stats(struct blkcg_gq *blkg)
+/* @stats = 0 */
+static void cfqg_stats_reset(struct cfqg_stats *stats)
 {
-	struct cfq_group *cfqg = blkg_to_cfqg(blkg);
-	struct cfqg_stats *stats = &cfqg->stats;
-
 	/* queued stats shouldn't be cleared */
 	blkg_rwstat_reset(&stats->service_bytes);
 	blkg_rwstat_reset(&stats->serviced);
@@ -1477,6 +1475,13 @@ static void cfq_pd_init(struct blkcg_gq *blkg)
 	cfqg->leaf_weight = blkg->blkcg->cfq_leaf_weight;
 }
 
+static void cfq_pd_reset_stats(struct blkcg_gq *blkg)
+{
+	struct cfq_group *cfqg = blkg_to_cfqg(blkg);
+
+	cfqg_stats_reset(&cfqg->stats);
+}
+
 /*
  * Search for the cfq group current task belongs to. request_queue lock must
  * be held.