blkcg: remove unnecessary request_list->blkg NULL test in blk_put_rl()

Since ec13b1d6 ("blkcg: always create the blkcg_gq for the root
blkcg"), a request_list always has its blkg associated.  Drop
unnecessary rl->blkg NULL test from blk_put_rl().
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

include/linux/blk-cgroup.h

@@ -394,8 +394,7 @@ static inline struct request_list *blk_get_rl(struct request_queue *q,
  */
 static inline void blk_put_rl(struct request_list *rl)
 {
-	/* root_rl may not have blkg set */
-	if (rl->blkg && rl->blkg->blkcg != &blkcg_root)
+	if (rl->blkg->blkcg != &blkcg_root)
 		blkg_put(rl->blkg);
 }