usb: dwc2: Fix UDC state tracking

It has been noticed that the dwc2 udc state reporting doesn't
seem to work (at least on HiKey boards). Where after the initial
setup, the sysfs /sys/class/udc/f72c0000.usb/state file would
report "configured" no matter the state of the OTG port.

This patch adds a call so that we report to the UDC layer when
the gadget device is disconnected.

This patch does depend on the previous patch ("usb: dwc2:
Improve gadget state disconnection handling") in this patch set
in order to properly work.

Cc: Wei Xu <xuwei5@hisilicon.com>
Cc: Guodong Xu <guodong.xu@linaro.org>
Cc: Amit Pundir <amit.pundir@linaro.org>
Cc: YongQin Liu <yongqin.liu@linaro.org>
Cc: John Youn <johnyoun@synopsys.com>
Cc: Minas Harutyunyan <Minas.Harutyunyan@synopsys.com>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Chen Yu <chenyu56@huawei.com>
Cc: Felipe Balbi <felipe.balbi@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Acked-by: Minas Harutyunyan <hminas@synopsys.com>
Tested-by: Minas Harutyunyan <hminas@synopsys.com>
Reported-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/dwc2/gadget.c

@@ -3202,6 +3202,8 @@ void dwc2_hsotg_disconnect(struct dwc2_hsotg *hsotg)
 
 	call_gadget(hsotg, disconnect);
 	hsotg->lx_state = DWC2_L3;
+
+	usb_gadget_set_state(&hsotg->gadget, USB_STATE_NOTATTACHED);
 }
 
 /**