fix build

src/main.rs

@@ -195,9 +195,15 @@ mod app {
             USB_BUS.replace(UsbBus::new(usb, &mut EP_MEMORY));
         }
 
-        let usb_serial = usbd_serial::SerialPort::new(unsafe { USB_BUS.as_ref().unwrap() });
+        let usb_serial = usbd_serial::SerialPort::new(unsafe {
+            #[allow(static_mut_refs)]
+            USB_BUS.as_ref().unwrap()
+        });
         let usb_dev = UsbDeviceBuilder::new(
-            unsafe { USB_BUS.as_ref().unwrap() },
+            unsafe {
+                #[allow(static_mut_refs)]
+                USB_BUS.as_ref().unwrap()
+            },
             UsbVidPid(0x16c0, 0x27dd),
         )
         .manufacturer("cats.radio")