usb: dwc3: gadget: set request dma to invalid when unmapping

if we don't set DMA address to invalid when unmapping,
we might fall in a situation where request buffer
can't be mapped to DMA again.
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/gadget.c

@@ -83,6 +83,7 @@ void dwc3_unmap_buffer_from_dma(struct dwc3_request *req)
 				req->request.length, req->direction
 				? DMA_TO_DEVICE : DMA_FROM_DEVICE);
 		req->mapped = 0;
+		req->request.dma = DMA_ADDR_INVALID;
 	} else {
 		dma_sync_single_for_cpu(dwc->dev, req->request.dma,
 				req->request.length, req->direction