util/vfio-helpers: Pass Error handle to qemu_vfio_dma_map()

Currently qemu_vfio_dma_map() displays errors on stderr.
When using management interface, this information is simply
lost. Pass qemu_vfio_dma_map() an Error** handle so it can
propagate the error to callers.

Reviewed-by: Fam Zheng <fam@euphon.net>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20210902070025.197072-7-philmd@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>