usb: Remove unused variable in usb_setup_descriptor()

The compiler did not catch this as it was marked __maybe_unused.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
diff --git a/common/usb.c b/common/usb.c
index 6283f39..7ff8ac5 100644
--- a/common/usb.c
+++ b/common/usb.c
@@ -959,8 +959,6 @@
 
 static int usb_setup_descriptor(struct usb_device *dev, bool do_read)
 {
-	__maybe_unused struct usb_device_descriptor *desc;
-
 	/*
 	 * This is a Windows scheme of initialization sequence, with double
 	 * reset of the device (Linux uses the same sequence)