usb: gadget: mv_u3d_core: fix violation of locking discipline in mv_u3d_ep_disable()

mv_u3d_nuke() expects to be calles with ep->u3d->lock held,
because mv_u3d_done() does. But mv_u3d_ep_disable() calls it
without lock that can lead to unpleasant consequences.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/mv_u3d_core.c

@@ -645,6 +645,7 @@ static int  mv_u3d_ep_disable(struct usb_ep *_ep)
 	struct mv_u3d_ep *ep;
 	struct mv_u3d_ep_context *ep_context;
 	u32 epxcr, direction;
+	unsigned long flags;
 
 	if (!_ep)
 		return -EINVAL;
@@ -661,7 +662,9 @@ static int  mv_u3d_ep_disable(struct usb_ep *_ep)
 	direction = mv_u3d_ep_dir(ep);
 
 	/* nuke all pending requests (does flush) */
+	spin_lock_irqsave(&u3d->lock, flags);
 	mv_u3d_nuke(ep, -ESHUTDOWN);
+	spin_unlock_irqrestore(&u3d->lock, flags);
 
 	/* Disable the endpoint for Rx or Tx and reset the endpoint type */
 	if (direction == MV_U3D_EP_DIR_OUT) {