blk-mq: turn hctx->run_work into a regular work struct

We don't need the larger delayed work struct, since we always run it
immediately.

Signed-off-by: Jens Axboe <axboe@fb.com>

include/linux/blk-mq.h

@@ -25,7 +25,7 @@ struct blk_mq_hw_ctx {
 	} ____cacheline_aligned_in_smp;
 
 	unsigned long		state;		/* BLK_MQ_S_* flags */
-	struct delayed_work	run_work;
+	struct work_struct	run_work;
 	struct delayed_work	delay_work;
 	cpumask_var_t		cpumask;
 	int			next_cpu;