usb: ohci-hcd: annotate switch/case fallthrough

The USB OCHI code uses an implicit switch/case fallthrough after checking
for valid descriptor IDs.

Add our "fallthrough;" statement-like macro before the default branch in
the OHCI code, to avoid a warning when GCC's -Wimplicit-fallthrough
warning option is enabled.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>

drivers/usb/host/ohci-hcd.c

@@ -1361,7 +1361,8 @@ pkt_print(ohci, NULL, dev, pipe, buffer, transfer_len,
 						wLength));
 				databuf = root_hub_str_index1;
 				OK(len);
-		}
+			}
+			fallthrough;
 		default:
 			stat = USB_ST_STALLED;
 		}