nvmet: cleanups the loop in nvmet_async_events_process

Based-on-a-patch-by: Christoph Hellwig <hch@infradead.org>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: David Milburn <dmilburn@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>