pbio/platform/prime_hub: set usb product name

This helps us find the hub in pybricksdev

Author: laurensvalk

lib/pbio/platform/prime_hub/usbd_desc.c

@@ -52,7 +52,7 @@
 #define USBD_PID                      0x5740
 #define USBD_LANGID_STRING            0x409
 #define USBD_MANUFACTURER_STRING      "STMicroelectronics"
-#define USBD_PRODUCT_FS_STRING        "STM32 Virtual ComPort in FS Mode"
+#define USBD_PRODUCT_FS_STRING        "Pybricks Hub"
 #define USBD_CONFIGURATION_FS_STRING  "VCP Config"
 #define USBD_INTERFACE_FS_STRING      "VCP Interface"