usb: dwc3: avoid -Wmaybe-uninitialized warning

Cleaning up the loop in dwc3_cleanup_done_reqs() introduced a
gcc warning if built with "-Wmaybe-uninitialized":

drivers/usb/dwc3/gadget.c: In function 'dwc3_endpoint_transfer_complete':
drivers/usb/dwc3/gadget.c:2015:9: 'trb' may be used uninitialized in this function [-Wmaybe-uninitialized]

I believe it is a false positive and we always have a valid 'trb'
pointer at the end of the function, but neither I nor the compiler
are able to prove that.

This works around the warning by computing a flag earlier in the function
when it's guaranteed to be valid, which tells the compiler that it's
safe and makes it easier to understand to me.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 31162af4 ("usb: dwc3: gadget: avoid while (1) loop on completion")
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -1934,6 +1934,7 @@ static int dwc3_cleanup_done_reqs(struct dwc3 *dwc, struct dwc3_ep *dep,
 {
 	struct dwc3_request	*req, *n;
 	struct dwc3_trb		*trb;
+	bool			ioc = false;
 	int			ret;
 
 	list_for_each_entry_safe(req, n, &dep->started_list, list) {
@@ -1981,9 +1982,13 @@ static int dwc3_cleanup_done_reqs(struct dwc3 *dwc, struct dwc3_ep *dep,
 
 		dwc3_gadget_giveback(dep, req, status);
 
-		if (ret)
+		if (ret) {
+			if ((event->status & DEPEVT_STATUS_IOC) &&
+			    (trb->ctrl & DWC3_TRB_CTRL_IOC))
+				ioc = true;
 			break;
 		}
+	}
 
 	/*
 	 * Our endpoint might get disabled by another thread during
@@ -2010,10 +2015,9 @@ static int dwc3_cleanup_done_reqs(struct dwc3 *dwc, struct dwc3_ep *dep,
 		return 1;
 	}
 
-	if (usb_endpoint_xfer_isoc(dep->endpoint.desc))
-		if ((event->status & DEPEVT_STATUS_IOC) &&
-				(trb->ctrl & DWC3_TRB_CTRL_IOC))
+	if (usb_endpoint_xfer_isoc(dep->endpoint.desc) && ioc)
 		return 0;
+
 	return 1;
 }