staging: octeon-hcd: remove unnecessary unlikely()

WARN_ON() already contains an unlikely(), so it's not necessary to
wrap it into another.

Signed-off-by: Igor Stoppa <igor.stoppa@huawei.com>
Cc: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: devel@driverdev.osuosl.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>