nvme/ioctl: don't warn on vectorized uring_cmd with fixed buffer

The vectorized io_uring NVMe passthru opcodes don't yet support fixed
buffers. But since userspace can trigger this condition based on the
io_uring SQE parameters, it shouldn't cause a kernel warning.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Fixes: 23fd22e5 ("nvme: wire up fixed buffer support for nvme passthrough")
Signed-off-by: Keith Busch <kbusch@kernel.org>