usb: dwc3: gadget: clear stall when disabling endpoint

commit 687ef9817df7ed960d14575b9033dde3d04631fe upstream.

so it seems like DWC3 IP doesn't clear stalls
automatically when we disable an endpoint, because
of that, we _must_ make sure stalls are cleared
before clearing the proper bit in DALEPENA register.

Reported-by: Johannes Stezenbach <js@sig21.net>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>