NVMe: Fix nvmeq waitqueue entry initialization

We need to update the nvme queue's wait_queue_t entry during each
initialization since the nvme_thread may be ended and restarted when
the device is reset. If a device reset occurs during a large amount
of buffered IO, it would take a lot longer to complete the outstanding
requests due to the 1 second polling instead of waking up as completions
occur.

Fixes: b9afca3e

Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>