nvme: change nvme_passthru_cmd64 to explicitly mark rsvd

nvme: change nvme_passthru_cmd64 to explicitly mark rsvd

Changing nvme_passthru_cmd64 to add a field: rsvd2. This field is an explicit
marker for the padding space added on certain platforms as a result of the
enlargement of the result field from 32 bit to 64 bits in size, and
fixes differences in struct size when using compat ioctl for 32-bit
binaries on 64-bit architecture.

Fixes: 65e68edce0db ("nvme: allow 64-bit results in passthru commands")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Charles Machalow <csm10495@gmail.com>
[changelog]
Signed-off-by: Keith Busch <kbusch@kernel.org>