nvmet: the result field in nvmet_alloc_ctrl_args is little endian

So use the __le32 type for it.

Fixes: 62027831 ("nvmet: Improve nvmet_alloc_ctrl() interface and implementation")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>