nvmet: use nvme status value directly

There is no point in keeping the status variable that is used only once
in the function nvmet_async_events_failall().

Remove the variable and use the value directly.

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>