ec/kontron/kempld: Add fall-through comments where appropriate

Fixes related GCC warnings.

Change-Id: I803fc0e005390ebd8a5e3ac6886ee968c56c3a34
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35473
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/ec/kontron/kempld/kempld.c

@@ -95,11 +95,13 @@ static void kempld_enable_dev(struct device *const dev)
 				dev->ops = &kempld_uart_ops;
 				break;
 			}
+			/* Fall through. */
 		case 1:
 			if (dev->path.generic.subid == 0) {
 				kempld_i2c_device_init(dev);
 				break;
 			}
+			/* Fall through. */
 		default:
 			printk(BIOS_WARNING,
 			       "KEMPLD: Spurious device %s.\n",