usb: dwc3: gadget: simplify next_request() return check

In dwc3_cleanup_done_reqs() we expect that all
iterations of our while (1) loop will find a valid
struct dwc3_request *. In case we don't, we're
dumping a WARN_ON_ONCE() splat so that people report
the failure.

This patch is a simple cleanup converting:

	if (!req) {
		WARN_ON_ONCE(1);
		return 1;
	}

to:

	if (WARN_ON_ONCE(!req))
		return 1;

which is a little easier to read.
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/gadget.c

@@ -1885,10 +1885,9 @@ static int dwc3_cleanup_done_reqs(struct dwc3 *dwc, struct dwc3_ep *dep,
 
 	do {
 		req = next_request(&dep->req_queued);
-		if (!req) {
-			WARN_ON_ONCE(1);
+		if (WARN_ON_ONCE(!req))
 			return 1;
-		}
+
 		i = 0;
 		do {
 			slot = req->start_slot + i;