pata_cmd64x: Use fallthrough pseudo-keyword

Replace /* FALL THRU */ comment with the new pseudo-keyword macro
fallthrough[1].

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-throughSigned-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/ata/pata_cmd64x.c

@@ -461,7 +461,7 @@ static int cmd64x_init_one(struct pci_dev *pdev, const struct pci_device_id *id)
 		case 1:
 			ppi[0] = &cmd_info[4];
 			ppi[1] = &cmd_info[4];
-			/* FALL THRU */
+			fallthrough;
 		/* Early revs have no CNTRL_CH0 */
 		case 2:
 		case 0: