blk-mq: fix potential deadlock while nr_requests grown

In the Linux kernel, the following vulnerability has been resolved: blk-mq: fix potential deadlock while nr_requests grown Allocate and free sched_tags while queue is freezed can deadlock[1], this is a long term problem, hence allocate memory before freezing queue and free memory after queue is unfreezed. [1] https://lore.kernel.org/all/0659ea8d-a463-47c8-9180-43c719e106eb@linux.ibm.com/