make control buf static

src/device/usbd_control.c

@@ -51,7 +51,7 @@ typedef struct
 
 static usbd_control_xfer_t _ctrl_xfer;
 
-CFG_TUSB_MEM_SECTION CFG_TUSB_MEM_ALIGN uint8_t _usbd_ctrl_buf[CFG_TUD_ENDPOINT0_SIZE];
+CFG_TUSB_MEM_SECTION CFG_TUSB_MEM_ALIGN static uint8_t _usbd_ctrl_buf[CFG_TUD_ENDPOINT0_SIZE];
 
 
 //--------------------------------------------------------------------+