nvme-pci: don't try to use SGLs for metadata on the admin queue

nvme-pci: don't try to use SGLs for metadata on the admin queue

No admin command defined in an NVMe specification supports metadata,
but to protect against vendor specific commands using metadata ensure
that we don't try to use SGLs for metadata on the admin queue, as NVMe
does not support SGLs on the admin queue for the PCI transport.  Do
this by checking if the data transfer has been setup using SGLs as
that is required for using SGLs for metadata.

Signed-off-by: Christoph Hellwig <hch@lst.de>