virtio-blk: improve virtqueue error to BLK_STS

Let's change the mapping between virtqueue_add errors to BLK_STS
statuses, so that -ENOSPC, which indicates virtqueue full is still
mapped to BLK_STS_DEV_RESOURCE, but -ENOMEM which indicates non-device
specific resource outage is mapped to BLK_STS_RESOURCE.

Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Link: https://lore.kernel.org/r/20200213123728.61216-3-pasic@linux.ibm.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>