mtd_blkdevs: initialze new->rq in add_mtd_blktrans_dev

Various places expect the request_queue in ->rq.  Initialize it to
avoid NULL pointer derefences.

Fixes: 6966bb9 ("mtd_blkdevs: use blk_mq_alloc_disk")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/mtd/mtd_blkdevs.c

@@ -382,6 +382,7 @@ int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
 	}
 
 	new->disk = gd;
+	new->rq = new->disk->queue;
 	gd->private_data = new;
 	gd->major = tr->major;
 	gd->first_minor = (new->devnum) << tr->part_bits;