usb: gadget: dummy_hcd: fix rescan logic for transfer

transfer() schedules a rescan for transfers larger than
maxpacket, which is wrong for transfers that are multiples
of maxpacket.

Rewrite to fix and clarify packet multiple / remainder
transfer logic.
Signed-off-by: NIgor Kotrasinski <i.kotrasinsk@samsung.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>

drivers/usb/gadget/udc/dummy_hcd.c

@@ -1385,12 +1385,15 @@ static int transfer(struct dummy_hcd *dum_hcd, struct urb *urb,
 			if (len == 0)
 				break;
 
-			/* use an extra pass for the final short packet */
-			if (len > ep->ep.maxpacket) {
-				rescan = 1;
-				len -= (len % ep->ep.maxpacket);
+			/* send multiple of maxpacket first, then remainder */
+			if (len >= ep->ep.maxpacket) {
+				is_short = 0;
+				if (len % ep->ep.maxpacket)
+					rescan = 1;
+				len -= len % ep->ep.maxpacket;
+			} else {
+				is_short = 1;
 			}
-			is_short = (len % ep->ep.maxpacket) != 0;
 
 			len = dummy_perform_transfer(urb, req, len);