blk-mq: don't access request_wrapper if request is not allocated from block layer

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I65K8D


CVE: NA

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request_wrapper is used to fix kabi broken for request, it's only for
internal use. This patch make sure out-of-tree drivers won't access
request_wrapper if request is not managed by block layer.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>