nvme: remove __nvme_ioctl

Open code __nvme_ioctl in the two callers to make future changes that
pass down additional paramters in the ioctl path easier.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Kanchan Joshi <joshi.k@samsung.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>