test(uhci): fix false-pass bug in UHCI receive test

reset RX buffer state between UHCI test transactions

components/esp_driver_uart/test_apps/uhci/main/test_uhci.c

@@ -157,6 +157,8 @@ static void uhci_receive_test(void *arg)
         }
 
         ctx->receive_size = 0;
+        ctx->p_receive_data = receive_data;
+        memset(receive_data, 0, DATA_LENGTH);
     }
 
     vQueueDelete(ctx->uhci_queue);