usb: udc: Fix warnings on 64-bit builds

Cast u32 bit value to 64bit before recasting to 64bit pointer to avoid
pointer from integer cast size mismatch warnings.

Warning log:
+../drivers/usb/gadget/udc/udc-core.c: In function
‘usb_gadget_unmap_request’:
+../drivers/usb/gadget/udc/udc-core.c:68:19: warning: cast to pointer
from integer of different size [-Wint-to-pointer-cast]

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

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

@@ -65,7 +65,7 @@ void usb_gadget_unmap_request(struct usb_gadget *gadget,
 	if (req->length == 0)
 		return;
 
-	dma_unmap_single((void *)req->dma, req->length,
+	dma_unmap_single((void *)(uintptr_t)req->dma, req->length,
 			 is_in ? DMA_TO_DEVICE : DMA_FROM_DEVICE);
 }
 EXPORT_SYMBOL_GPL(usb_gadget_unmap_request);