cleanup: Remove implicit fallthrough in CRC validation

Firmware/mmu2_protocol.cpp

@@ -112,6 +112,10 @@ DecodeStatus Protocol::DecodeRequest(uint8_t c) {
                 rqState = RequestStates::Code;
                 return DecodeStatus::MessageCompleted;
             }
+        } else {
+            requestMsg.code = RequestMsgCodes::unknown;
+            rqState = RequestStates::Error;
+            return DecodeStatus::Error;
         }
     default: //case error:
         if (IsNewLine(c)) {