NVMe: nvme_core_exit() should do cleanup in the reverse order as nvme_core_init does

nvme_core_init does:
    1) register_blkdev
    2) __register_chrdev
    3) class_create

nvme_core_exit should do cleanup in the reverse order.

Signed-off-by: Wang Sheng-Hui <shhuiw@foxmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/nvme/host/core.c

@@ -1715,9 +1715,9 @@ int __init nvme_core_init(void)
 
 void nvme_core_exit(void)
 {
-	unregister_blkdev(nvme_major, "nvme");
 	class_destroy(nvme_class);
 	__unregister_chrdev(nvme_char_major, 0, NVME_MINORS, "nvme");
+	unregister_blkdev(nvme_major, "nvme");
 }
 
 MODULE_LICENSE("GPL");