remove compiler warning about passing NULL to non-pointer argument

Author: stevstrong

STM32F1/cores/maple/usb_serial.cpp

@@ -71,7 +71,7 @@ void USBSerial::begin(void) {
         return;
     _hasBegun = true;
 
-    usb_cdcacm_enable(BOARD_USB_DISC_DEV, BOARD_USB_DISC_BIT);
+    usb_cdcacm_enable(BOARD_USB_DISC_DEV, (uint8_t)BOARD_USB_DISC_BIT);
     usb_cdcacm_set_hooks(USB_CDCACM_HOOK_RX, rxHook);
     usb_cdcacm_set_hooks(USB_CDCACM_HOOK_IFACE_SETUP, ifaceSetupHook);
 #endif
@@ -97,7 +97,7 @@ volatile uint8_t removeCompilerWarningsIgnore=ignore;
 
 void USBSerial::end(void) {
 #if BOARD_HAVE_SERIALUSB
-    usb_cdcacm_disable(BOARD_USB_DISC_DEV, BOARD_USB_DISC_BIT);
+    usb_cdcacm_disable(BOARD_USB_DISC_DEV, (uint8_t)BOARD_USB_DISC_BIT);
     usb_cdcacm_remove_hooks(USB_CDCACM_HOOK_RX | USB_CDCACM_HOOK_IFACE_SETUP);
 	_hasBegun = false;
 #endif