block: remove set but not used variable 'et'

Fixes gcc '-Wunused-but-set-variable' warning:

block/blk-ioc.c: In function 'put_io_context_active':
block/blk-ioc.c:174:24: warning:
 variable 'et' set but not used [-Wunused-but-set-variable]

It not used any more after commit
a1ce35fa ("block: remove dead elevator code")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-ioc.c

@@ -171,7 +171,6 @@ EXPORT_SYMBOL(put_io_context);
  */
 void put_io_context_active(struct io_context *ioc)
 {
-	struct elevator_type *et;
 	unsigned long flags;
 	struct io_cq *icq;
 
@@ -190,7 +189,6 @@ void put_io_context_active(struct io_context *ioc)
 		if (icq->flags & ICQ_EXITED)
 			continue;
 
-		et = icq->q->elevator->type;
 		ioc_exit_icq(icq);
 	}
 	spin_unlock_irqrestore(&ioc->lock, flags);