treewide: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
fall-through markings when it is the case.

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index ca1c39b..3b18034 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -148,7 +148,7 @@ static void virtscsi_complete_cmd(struct virtio_scsi *vscsi, void *buf)
 	default:
 		scmd_printk(KERN_WARNING, sc, "Unknown response %d",
 			    resp->response);
-		/* fall through */
+		fallthrough;
 	case VIRTIO_SCSI_S_FAILURE:
 		set_host_byte(sc, DID_ERROR);
 		break;