usb: dwc3: gadget: Fix null pointer exception

In the endpoint interrupt functions
dwc3_gadget_endpoint_transfer_in_progress() and
dwc3_gadget_endpoint_trbs_complete() will dereference the endpoint
descriptor. But it could be cleared in __dwc3_gadget_ep_disable()
when accessory disconnected. So we need to check whether it is null
or not before dereferencing it.

Fixes: f09ddcfcb8c5 ("usb: dwc3: gadget: Prevent EP queuing while stopping transfers")
Cc: stable <[e-mail]>
Reviewed-by: Jack Pham <[e-mail]>
Signed-off-by: Albert Wang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/dwc3/gadget.c

···
 	struct dwc3		*dwc = dep->dwc;
 	bool			no_started_trb = true;
 
+	if (!dep->endpoint.desc)
+		return no_started_trb;
+
 	dwc3_gadget_ep_cleanup_completed_requests(dep, event, status);
 
 	if (dep->flags & DWC3_EP_END_TRANSFER_PENDING)
···
 		const struct dwc3_event_depevt *event)
 {
 	int status = 0;
+
+	if (!dep->endpoint.desc)
+		return;
 
 	if (usb_endpoint_xfer_isoc(dep->endpoint.desc))
 		dwc3_gadget_endpoint_frame_from_event(dep, event);