blk-mq: decrease pending_queues when it expires

hulk inclusion
category: performance
bugzilla: https://gitee.com/openeuler/kernel/issues/I4S8DW



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If pending_queues is increased once, it will only be decreased when
nr_active is zero, and that will lead to the under-utilization of
host tags because pending_queues is non-zero and the available
tags for the queue will be max(host tags / active_queues, 4)
instead of the needed tags of the queue.

Fix it by adding an expiration time for the increasement of pending_queues,
and decrease it when it expires, so pending_queues will be decreased
to zero if there is no tag allocation failure, and the available tags
for the queue will be the whole host tags.

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