Clear streaming flag if a transfer was cancelled.

If a transfer was cancelled, we are on our way to shutdown.

If hackrf_stop_tx() or hackrf_stop_rx() were called, they will already
have cleared this flag, but it is not cleared in hackrf_close(), and
for consistency with other paths it makes sense to clear it here.

host/libhackrf/src/hackrf.c

@@ -1762,6 +1762,7 @@ static void LIBUSB_CALL hackrf_libusb_transfer_callback(struct libusb_transfer*
 		}
 	} else if(usb_transfer->status == LIBUSB_TRANSFER_CANCELLED) {
 		transfer_finished(device, usb_transfer);
+		device->streaming = false;
 	} else {
 		/* Other cases LIBUSB_TRANSFER_NO_DEVICE
 		LIBUSB_TRANSFER_ERROR, LIBUSB_TRANSFER_TIMED_OUT