usb: chipidea: udc: fix memory leak in _ep_nuke

In hardware_enqueue code adds one extra td with dma_pool_alloc if
mReq->req.zero is true. When _ep_nuke will be called for that endpoint,
dma_pool_free will not be called to free that memory again. That patch
fixes this.

Cc: stable <stable@vger.kernel.org> # v3.5
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>