storvsc: be more picky about scmnd->sc_data_direction

Under the 'default' case in scmnd->sc_data_direction we have 3 options:
- DMA_NONE which we handle correctly.
- DMA_BIDIRECTIONAL which is never supposed to be set by SCSI stack.
- Garbage value.

Do WARN() and return -EINVAL in the last two cases. virtio_scsi does
BUG_ON() here but it looks like an overkill.
Reported-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Acked-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>

drivers/scsi/storvsc_drv.c

@@ -1598,10 +1598,18 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
 		vm_srb->data_in = READ_TYPE;
 		vm_srb->win8_extension.srb_flags |= SRB_FLAGS_DATA_IN;
 		break;
-	default:
+	case DMA_NONE:
 		vm_srb->data_in = UNKNOWN_TYPE;
 		vm_srb->win8_extension.srb_flags |= SRB_FLAGS_NO_DATA_TRANSFER;
 		break;
+	default:
+		/*
+		 * This is DMA_BIDIRECTIONAL or something else we are never
+		 * supposed to see here.
+		 */
+		WARN(1, "Unexpected data direction: %d\n",
+		     scmnd->sc_data_direction);
+		return -EINVAL;
 	}