net: usb: Mark expected switch fall-throughs

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

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

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 drivers/net/usb/catc.c       | 1 +
 drivers/net/usb/cdc-phonet.c | 1 +
 drivers/net/usb/r8152.c      | 2 ++
 3 files changed, 4 insertions(+)

diff --git a/drivers/net/usb/catc.c b/drivers/net/usb/catc.c
index 18d36df..424053b 100644
--- a/drivers/net/usb/catc.c
+++ b/drivers/net/usb/catc.c
@@ -869,6 +869,7 @@ static int catc_probe(struct usb_interface *intf, const struct usb_device_id *id
 		default:
 			dev_warn(&intf->dev,
 				 "Couldn't detect memory size, assuming 32k\n");
+			/* fall through */
 		case 0x87654321:
 			catc_set_reg(catc, TxBufCount, 4);
 			catc_set_reg(catc, RxBufCount, 16);
diff --git a/drivers/net/usb/cdc-phonet.c b/drivers/net/usb/cdc-phonet.c
index 3c40312..78b16eb 100644
--- a/drivers/net/usb/cdc-phonet.c
+++ b/drivers/net/usb/cdc-phonet.c
@@ -110,6 +110,7 @@ static void tx_complete(struct urb *req)
 	case -ECONNRESET:
 	case -ESHUTDOWN:
 		dev->stats.tx_aborted_errors++;
+		/* fall through */
 	default:
 		dev->stats.tx_errors++;
 		dev_dbg(&dev->dev, "TX error (%d)\n", status);
diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
index 1fd1650..124211a 100644
--- a/drivers/net/usb/r8152.c
+++ b/drivers/net/usb/r8152.c
@@ -1376,6 +1376,7 @@ static void intr_callback(struct urb *urb)
 	case -ECONNRESET:	/* unlink */
 	case -ESHUTDOWN:
 		netif_device_detach(tp->netdev);
+		/* fall through */
 	case -ENOENT:
 	case -EPROTO:
 		netif_info(tp, intr, tp->netdev,
@@ -2741,6 +2742,7 @@ static void r8153b_ups_en(struct r8152 *tp, bool enable)
 			r8152_mdio_write(tp, MII_BMCR, data);
 
 			data = r8153_phy_status(tp, PHY_STAT_LAN_ON);
+			/* fall through */
 
 		default:
 			if (data != PHY_STAT_LAN_ON)