scsi: virtio-scsi: Correctly handle the case where all LUNs are unplugged

scsi: virtio-scsi: Correctly handle the case where all LUNs are unplugged

Commit 5ff843721467 ("scsi: virtio_scsi: unplug LUNs when events missed")
missed a corner case in which all the LUNs are unplugged at the same time.

In this case INQUIRY returns DID_BAD_TARGET. Detect this and unplug the
LUN.

Link: https://lore.kernel.org/r/20200729194806.4933-2-mlevitsk@redhat.com
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>