fotg210-udc: Fix DMA on EP0 for length > max packet size

For a 75 Byte request, it would send the first 64 separately, then detect
that the remaining 11 Byte fit into a single DMA, but due to this bug set
the length to the original 75 Bytes. This leads to a DMA failure (which is
ignored...) and the request completes without the remaining bytes having
been sent.

Fixes: b84a8dee ("usb: gadget: add Faraday fotg210_udc driver")
Signed-off-by: Fabian Vogt <fabian@ritter-vogt.de>
Link: https://lore.kernel.org/r/20210324141115.9384-2-fabian@ritter-vogt.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/udc/fotg210-udc.c

@@ -346,7 +346,7 @@ static void fotg210_start_dma(struct fotg210_ep *ep,
 		if (req->req.length - req->req.actual > ep->ep.maxpacket)
 			length = ep->ep.maxpacket;
 		else
-			length = req->req.length;
+			length = req->req.length - req->req.actual;
 	}
 
 	d = dma_map_single(dev, buffer, length,