usb: gadget: Add missing annotation for xudc_handle_setup()

Sparse reports a warning at xudc_handle_setup()

warning: context imbalance in xudc_handle_setup() - unexpected unlock

The root cause is the missing annotation at xudc_handle_setup()

Add the missing __must_hold(&udc->lock) annotation
Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

drivers/usb/gadget/udc/udc-xilinx.c

@@ -1732,6 +1732,7 @@ static void xudc_set_clear_feature(struct xusb_udc *udc)
  * Process setup packet and delegate to gadget layer.
  */
 static void xudc_handle_setup(struct xusb_udc *udc)
+	__must_hold(&udc->lock)
 {
 	struct xusb_ep *ep0 = &udc->ep[0];
 	struct usb_ctrlrequest setup;