phylink: mark expected switch fall-throughs in phylink_mii_ioctl

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

Addresses-Coverity-ID: 1463447 ("Missing break in switch")
Signed-off-by: NGustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/phy/phylink.c

@@ -1296,6 +1296,7 @@ int phylink_mii_ioctl(struct phylink *pl, struct ifreq *ifr, int cmd)
 		switch (cmd) {
 		case SIOCGMIIPHY:
 			mii->phy_id = pl->phydev->mdio.addr;
+			/* fall through */
 
 		case SIOCGMIIREG:
 			ret = phylink_phy_read(pl, mii->phy_id, mii->reg_num);
@@ -1318,6 +1319,7 @@ int phylink_mii_ioctl(struct phylink *pl, struct ifreq *ifr, int cmd)
 		switch (cmd) {
 		case SIOCGMIIPHY:
 			mii->phy_id = 0;
+			/* fall through */
 
 		case SIOCGMIIREG:
 			ret = phylink_mii_read(pl, mii->phy_id, mii->reg_num);