net: ethernet: bgmac: mark expected switch fall-through

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

Addresses-Coverity-ID: 1397972
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/bgmac-platform.c

@@ -131,6 +131,7 @@ static void bgmac_nicpm_speed_set(struct net_device *net_dev)
 	switch (bgmac->net_dev->phydev->speed) {
 	default:
 		netdev_err(net_dev, "Unsupported speed. Defaulting to 1000Mb\n");
+		/* fall through */
 	case SPEED_1000:
 		val |= NICPM_IOMUX_CTRL_SPD_1000M << NICPM_IOMUX_CTRL_SPD_SHIFT;
 		break;