Use the fallthrough statement in switch loops

Clang does not seem to work with 'fall through' in comments.

Change-Id: Idcbe373be33ef7247548f856bfaba7ceb7f749b5
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51498
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

src/ec/google/chromeec/ec_acpi.c

@@ -111,7 +111,8 @@ static const char *port_location_to_str(enum ec_pd_port_location port_location)
 		return "BACK_LEFT";
 	case EC_PD_PORT_LOCATION_BACK_RIGHT:
 		return "BACK_RIGHT";
-	case EC_PD_PORT_LOCATION_UNKNOWN: /* intentional fallthrough */
+	case EC_PD_PORT_LOCATION_UNKNOWN:
+		__fallthrough;
 	default:
 		return "UNKNOWN";
 	}

src/ec/kontron/kempld/kempld.c

@@ -82,13 +82,13 @@ static void kempld_enable_dev(struct device *const dev)
 				dev->ops = &kempld_uart_ops;
 				break;
 			}
-			/* Fall through. */
+			__fallthrough;
 		case 1:
 			if (dev->path.generic.subid == 0) {
 				kempld_i2c_device_init(dev);
 				break;
 			}
-			/* Fall through. */
+			__fallthrough;
 		default:
 			printk(BIOS_WARNING, "KEMPLD: Spurious device %s.\n", dev_path(dev));
 			break;