[SCSI] virtio_scsi: fix memory leak on full queue condition.

virtscsi_queuecommand was leaking memory when the virtio queue was full.

Tested: Guest operates correctly even with very small queue sizes, validated
we're not leaking kmalloc-192 sized allocations anymore.
Signed-off-by: NEric Northup <digitaleric@google.com>
Acked-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NJames Bottomley <JBottomley@Parallels.com>

drivers/scsi/virtio_scsi.c

@@ -469,6 +469,8 @@ static int virtscsi_queuecommand(struct Scsi_Host *sh, struct scsi_cmnd *sc)
 			      sizeof cmd->req.cmd, sizeof cmd->resp.cmd,
 			      GFP_ATOMIC) >= 0)
 		ret = 0;
+	else
+		mempool_free(cmd, virtscsi_cmd_pool);
 
 out:
 	return ret;