nvme: fix misaccounting of nvme-mpath inflight I/O

Procedures for nvme-mpath IO accounting:

 1) initialize nvme_request and clear flags;
 2) set NVME_MPATH_IO_STATS and increase inflight counter when IO
    started;
 3) check NVME_MPATH_IO_STATS and decrease inflight counter when IO is
    done;

However, for the case nvme_fail_nonready_command(), both step 1) and 2)
are skipped, and if old nvme_request set NVME_MPATH_IO_STATS and then
request is reused, step 3) will still be executed, causing inflight I/O
counter to be negative.

Fix the problem by clearing nvme_request in nvme_fail_nonready_command().

Fixes: ea5e5f42 ("nvme-fabrics: avoid double completions in nvmf_fail_nonready_command")
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Closes: https://lore.kernel.org/all/CAHj4cs_+dauobyYyP805t33WMJVzOWj=7+51p4_j9rA63D9sog@mail.gmail.com/


Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>