net: 8390: pcnet_cs: mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Addresses-Coverity-ID: 114891
Signed-off-by: NGustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/8390/pcnet_cs.c

@@ -1107,6 +1107,7 @@ static int ei_ioctl(struct net_device *dev, struct ifreq *rq, int cmd)
     switch (cmd) {
     case SIOCGMIIPHY:
 	data->phy_id = info->phy_id;
+	/* fall through */
     case SIOCGMIIREG:		/* Read MII PHY register. */
 	data->val_out = mdio_read(mii_addr, data->phy_id, data->reg_num & 0x1f);
 	return 0;