dm: make sure dm_table is binded before queue request

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4U3RI


CVE: NA

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We found a NULL pointer dereference problem when using dm-mpath target.
The problem is if we submit IO between loading and binding the table,
we could neither get a valid dm_target nor a valid dm table when
submitting request in dm_mq_queue_rq(). BIO based dm target could
handle this case in dm_submit_bio(). This patch fix this by checking
the mapping table before submitting request.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>