nvme: add nvme_complete_req tracepoint for batched completion

Add NVMe request completion trace in nvme_complete_batch_req() because
nvme:nvme_complete_req tracepoint is missing in case of request batched
completion.

Signed-off-by: Bean Huo <beanhuo@micron.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>