atmel: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1].

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-throughSigned-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200821065355.GA25808@embeddedor

drivers/net/wireless/atmel/at76c50x-usb.c

@@ -432,7 +432,7 @@ static int at76_usbdfu_download(struct usb_device *udev, u8 *buf, u32 size,
 
 		case STATE_DFU_DOWNLOAD_IDLE:
 			at76_dbg(DBG_DFU, "DOWNLOAD...");
-			/* fall through */
+			fallthrough;
 		case STATE_DFU_IDLE:
 			at76_dbg(DBG_DFU, "DFU IDLE");
 

drivers/net/wireless/atmel/atmel.c

@@ -1227,7 +1227,7 @@ static irqreturn_t service_interrupt(int irq, void *dev_id)
 
 		case ISR_RxFRAMELOST:
 			priv->wstats.discard.misc++;
-			/* fall through */
+			fallthrough;
 		case ISR_RxCOMPLETE:
 			rx_done_irq(priv);
 			break;