USB: WUSBCORE: fix leak of urb in wa_xfer_destroy.

The check to free the URB was the opposite of the correct case.  This
patch removes the check altogether since the ptr will be NULL if the URB
was not allocated.  Also use usb_free_urb instead of usb_put_urb.

Signed-off-by: Thomas Pugliese <thomas.pugliese@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>