usb: dwc3: gadget: initialize max_streams

Without this the gadget will never be able to allocate a stream capable
endpoint. The manual says that the stream id is a 16bit id. It does not
talk about an upper limit in any other way. So I think 15 is a
reasonable limit :)
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/dwc3/gadget.c

@@ -1284,6 +1284,7 @@ static int __devinit dwc3_gadget_init_endpoints(struct dwc3 *dwc)
 			int		ret;
 
 			dep->endpoint.maxpacket = 1024;
+			dep->endpoint.max_streams = 15;
 			dep->endpoint.ops = &dwc3_gadget_ep_ops;
 			list_add_tail(&dep->endpoint.ep_list,
 					&dwc->gadget.ep_list);