usb: dwc3: fix for the isoc transfer EP_BUSY flag

commit f3af36511e60 ("usb: dwc3: gadget: always
enable IOC on bulk/interrupt transfers") ended up
regressing Isochronous endpoints by clearing
DWC3_EP_BUSY flag too early, which resulted in
choppy audio playback over USB.

Fix that by partially reverting original commit and
making sure that we check for isochronous endpoints.

Fixes: f3af36511e60 ("usb: dwc3: gadget: always enable IOC
		on bulk/interrupt transfers")
Cc: <stable@vger.kernel.org>
Signed-off-by: Konrad Leszczynski <konrad.leszczynski@intel.com>
Signed-off-by: Rafal Redzimski <rafal.f.redzimski@intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc3/gadget.c

@@ -2058,6 +2058,10 @@ 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))
+			return 0;
 	return 1;
 }