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/parport/parport_pc.c b/drivers/parport/parport_pc.c
index 77e37e3..eda4ded 100644
--- a/drivers/parport/parport_pc.c
+++ b/drivers/parport/parport_pc.c
@@ -1647,7 +1647,7 @@ static int parport_ECP_supported(struct parport *pb)
 		break;
 	default:
 		pr_warn("0x%lx: Unknown implementation ID\n", pb->base);
-		/* Fall through - Assume 1 */
+		fallthrough;	/* Assume 1 */
 	case 1:
 		pword = 1;
 	}