usb: gadget: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
fall-through markings when it is the case.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20200707171500.GA13620@embeddedor
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/f_printer.c

@@ -285,7 +285,7 @@ static void rx_complete(struct usb_ep *ep, struct usb_request *req)
 
 	/* data overrun */
 	case -EOVERFLOW:
-		/* FALLTHROUGH */
+		fallthrough;
 
 	default:
 		DBG(dev, "rx status %d\n", status);
@@ -304,7 +304,7 @@ static void tx_complete(struct usb_ep *ep, struct usb_request *req)
 	switch (req->status) {
 	default:
 		VDBG(dev, "tx err %d\n", req->status);
-		/* FALLTHROUGH */
+		fallthrough;
 	case -ECONNRESET:		/* unlink */
 	case -ESHUTDOWN:		/* disconnect etc */
 		break;
@@ -919,7 +919,7 @@ static bool gprinter_req_match(struct usb_function *f,
 		if (!w_value && !w_length &&
 		   !(USB_DIR_IN & ctrl->bRequestType))
 			break;
-		/* fall through */
+		fallthrough;
 	default:
 		return false;
 	}