nvme: fix error-handling for io_uring nvme-passthrough

Driver may return an error before submitting the command to the device.
Ensure that such error is propagated up.

Fixes: 456cba38 ("nvme: wire-up uring-cmd support for io-passthru on char-device.")
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
Reviewed-by: Niklas Cassel <niklas.cassel@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>