Call USBD_Disconnect before software-triggered CPU reset

This makes sure that we'll re-enumerate on the USB, as a CPU reset
apparently doesn't automatically release the pull-up and notify the hub
that we were gone?

firmware/libboard/qmod/source/board_qmod.c

@@ -112,6 +112,7 @@ void board_exec_dbg_cmd(int ch)
 		break;
 	case 'R':
 		printf("Asking NVIC to reset us\n\r");
+		USBD_Disconnect();
 		NVIC_SystemReset();
 		break;
 	case 'O':