i2c: designware-pcidrv: Mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.
Signed-off-by: NGustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-designware-pcidrv.c

@@ -105,6 +105,7 @@ static int mfld_setup(struct pci_dev *pdev, struct dw_pci_controller *c)
 	case 0x0817:
 		c->bus_cfg &= ~DW_IC_CON_SPEED_MASK;
 		c->bus_cfg |= DW_IC_CON_SPEED_STD;
+		/* fall through */
 	case 0x0818:
 	case 0x0819:
 		c->bus_num = pdev->device - 0x817 + 3;