hw/nvme: ensure sgl forward progress

A degenerate host can create segment loops of zero-byte data descriptors
that the controller never breaks out of. While the spec allows zero
length segments, it provides no guidance on handling loops. It
makes no sense for a host to submit such a descriptor anyway since it
can and trivially should point to the next transfer segment, so don't
even try to work with such behavior. Just reject the command,
terminating the loop.

Cc: qemu-stable@nongnu.org
Reported-by: Feifan Qian <bea1e@proton.me>
Reported-by: boy juju <agx1657748706@gmail.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>