usb: dwc2: Fix NULL qh in dwc2_queue_transaction

When a usb device disconnects in a certain way, dwc2_queue_transaction
still gets called after dwc2_hcd_cleanup_channels.

dwc2_hcd_cleanup_channels does "channel->qh = NULL;" but
dwc2_queue_transaction still wants to dereference qh.
This adds a check for a null qh.

Acked-by: Minas Harutyunyan <[e-mail]>
Signed-off-by: Alexandru M Stan <[e-mail]>
[dianders: rebased to mainline]
Signed-off-by: Douglas Anderson <[e-mail]>
Signed-off-by: Felipe Balbi <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/dwc2/hcd.c

···
 		list_move_tail(&chan->split_order_list_entry,
 			       &hsotg->split_order);
 
-	if (hsotg->params.host_dma) {
+	if (hsotg->params.host_dma && chan->qh) {
 		if (hsotg->params.dma_desc_enable) {
 			if (!chan->xfer_started ||
 			    chan->ep_type == USB_ENDPOINT_XFER_ISOC) {