silence some errors that is not actually an error

src/common.h

@@ -70,6 +70,7 @@ typedef libusb_device_handle *usb_device_handle_t;
 
 #define USB_RET_SUCCESS         LIBUSB_SUCCESS
 #define USB_RET_NOT_RESPONDING  LIBUSB_ERROR_OTHER
+#define USB_RET_IO				LIBUSB_ERROR_IO
 
 extern void* pongo_usb_callback(void* arg);
 usb_ret_t USBControlTransfer(usb_device_handle_t handle, uint8_t bmRequestType, uint8_t bRequest, uint16_t wValue, uint16_t wIndex, uint32_t wLength, void *data, uint32_t *wLenDone);

src/pongo_usb.c

@@ -373,6 +373,8 @@ bad:
 	{
 		if (ret == USB_RET_NOT_RESPONDING)
 			return 0;
+        if (!strncmp("boot", command, 4) && ret == USB_RET_IO)
+            return 0;
 		LOG(LOG_ERROR, "USB error: %s", usb_strerror(ret));
 		return ret;
 	}