net: 3com: 3c574_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: 114888
Signed-off-by: NGustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/3com/3c574_cs.c

@@ -1046,6 +1046,7 @@ static int el3_ioctl(struct net_device *dev, struct ifreq *rq, int cmd)
 	switch(cmd) {
 	case SIOCGMIIPHY:		/* Get the address of the PHY in use. */
 		data->phy_id = phy;
+		/* fall through */
 	case SIOCGMIIREG:		/* Read the specified MII register. */
 		{
 			int saved_window;