We should ensure that all resources of device are freed before gone.
In fact, upper layer can ensure that all upper layer IOs are finished
when get dev gone. But for some LLDD internal failed IOs, LLDD resources
may not freed. So, this patch release remain LLDD resources before dev
gone if there are.
Signed-off-by: NXiaofei Tan <tanxiaofei@huawei.com>