sys/uart_stdio: adapted to cb type change

sys/include/uart_stdio.h

@@ -81,7 +81,7 @@ int uart_stdio_write(const char* buffer, int len);
  * @param[in]   arg     (unused)
  * @param[in]   data    character that has been received
  */
-void uart_stdio_rx_cb(void *arg, char data);
+void uart_stdio_rx_cb(void *arg, uint8_t data);
 
 #ifdef __cplusplus
 }

sys/uart_stdio/uart_stdio.c

@@ -52,10 +52,10 @@ static tsrb_t _rx_buf = TSRB_INIT(_rx_buf_mem);
 /**
  * @brief Receive a new character from the UART and put it into the receive buffer
  */
-void uart_stdio_rx_cb(void *arg, char data)
+void uart_stdio_rx_cb(void *arg, uint8_t data)
 {
     (void)arg;
-    tsrb_add_one(&_rx_buf, data);
+    tsrb_add_one(&_rx_buf, (uint8_t)data);
     mutex_unlock(&_rx_mutex);
 }