x86/platform/olpc: Use PTR_ERR_OR_ZERO()

Replace the open coded equivalent with PTR_ERR_OR_ZERO().

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/1533053286-34990-1-git-send-email-zhongjiang@huawei.com